Best SIM-Only Deals for Heavy Data Users UK 2026

If you stream on the move, tether a laptop, or burn through more than 50GB of mobile data a month, you need a SIM-only deal built for it — not a mid-size bundle that runs dry by the 20th. This guide covers the best SIM-only deals for heavy data users in the UK: genuine unlimited data plans for your phone, and big 100GB-plus bundles for people who want a defined ceiling. Every price was checked on 6 September 2026, with honest notes on speed caps, hotspot rules and the April price rises that now apply to the big four.

The headline finding: the cheapest genuine unlimited data SIM now costs around £14–£15/mo (giffgaff’s limited-time promo, or iD Mobile’s standard 24-month plan), not the sub-£10 unlimited deal that floated around earlier in 2026 — that has gone. Our guide to SIM-only vs a phone contract runs the maths on whether SIM-only suits you; for every data tier including smaller plans, see the best SIM-only deals UK guide.

Last updated: 6 September 2026

One note on scope: this guide covers SIM deals for your phone. A data-only SIM for a tablet, a 4G/5G home router or a MiFi device is a different product with its own plans and pricing, so it isn’t covered here.

Quick comparison: best SIM-only deals for heavy data users (September 2026)

Unlimited data on your phone starts at around £14–£15/mo. Here is the at-a-glance view, ranked by our editorial rating. Big 100GB-plus non-unlimited plans are covered in their own section below.

Quick verdict cards

Best unlimited SIM deals for heavy data users UK 2026

Unlimited data is the right call if you regularly use more than 80–100GB a month, tether a laptop, or do not want to track a data counter. As of September 2026 the entry price is around £14–£15/mo, rising to the low £20s for flexible rolling plans and past £30 for EE’s premium coverage.

iD Mobile Unlimited — ~£15/mo (24-month, no price rise)

iD Mobile Unlimited is ~£15/mo on a 24-month contract (as of September 2026, source: iD Mobile) and it is the strongest all-round pick for heavy data users. You get genuinely unlimited data on Three’s network — the UK’s fastest average 5G — with no separate cap on tethering. iD Mobile states on its own site that it does not build in annual price rises, so the ~£15/mo you sign up at is what you pay in month 24 — unlike every one of the big four.

The trade-offs are minor: MVNO customers sit slightly behind direct Three during heavy congestion, roaming covers 50 destinations rather than 70-plus, and the best price needs the 24-month term. Via MoneySavingExpert, iD’s unlimited plan has recently come with a gift card that cuts the effective cost to around £12/mo — check for current voucher offers before buying direct.

giffgaff Unlimited — ~£14/mo promo (18-month) or ~£20/mo rolling

giffgaff’s unlimited goodybag is the cheapest genuine unlimited data deal right now at ~£14/mo on an 18-month term (as of September 2026, source: giffgaff). That is a promotional price — the standard rate is £25/mo — but giffgaff operates a price lock with no mid-contract rises, so ~£14/mo holds for the full term. It runs on O2’s network, solid for coverage but slower than Three and EE for average 5G.

If you would rather not commit for 18 months, giffgaff also sells unlimited on a one-month rolling basis at ~£20/mo (limited-time; standard £35) — matching Smarty and Three, but on O2. No credit check, tethering included. These are promotional figures from giffgaff’s goodybags page, so treat them as early-September 2026 and confirm on the day.

Smarty Unlimited — ~£20/mo (30-day rolling, no price rise)

Smarty Unlimited is ~£20/mo on a one-month rolling contract (as of September 2026, source: Smarty), and it is the pick if you want genuine unlimited with total flexibility. It runs on Three’s network — the same fast 5G as iD Mobile — and Smarty states “no annual price rises” on its own plans page. There is no hard speed cap, only fair-use management during congestion. Stop paying and the plan ends.

The downside versus iD Mobile is purely price: about £5/mo more for a rolling contract instead of a 24-month one, roughly £60 over a year. If you know you want unlimited long term, iD is cheaper; if you might switch again soon, Smarty is the low-risk way in. Smarty also sells 150GB at ~£15/mo and 200GB at ~£17/mo — see the non-unlimited section.

Three Unlimited — ~£20/mo (12-month), rising each April

Three’s own unlimited SIM is ~£20/mo on a 12-month contract (as of September 2026, source: Three via Uswitch), with a 24-month “Lite” version at the same headline price. There is no current “£8/mo unlimited” promotion — if you saw that earlier in 2026, it has ended; the nearest thing now is “six months half price” on selected 24-month plans. As a direct Three customer you get the highest congestion priority and roaming across 70-plus destinations — the main reasons to pick Three over iD Mobile or Smarty on the same masts.

The catch is the price rise. Three adds a fixed increase every 1 April: +£1.90/mo for 5–99GB plans, +£2.30/mo for 100GB-plus and unlimited. So ~£20/mo now becomes ~£22.30/mo from April 2027 and ~£24.60/mo from April 2028 on a 24-month term. Three’s unlimited is genuinely uncapped for personal use, so for very high-volume users it is worth the premium over the MVNOs. If price stability matters more, iD Mobile on the same network avoids the rises.

iD Mobile, giffgaff, Smarty and Three are featured editorially here — check each provider’s own site for the current unlimited price and any introductory offers.

Lebara Unlimited — ~£25/mo (30-day rolling), calls to 50+ countries

Lebara’s unlimited plan is ~£25/mo on a 30-day rolling contract (as of September 2026, source: Lebara) and it earns its place for one reason: every Lebara plan includes minutes to 50-plus countries as standard, not as an add-on. It runs on Vodafone’s network with 5G where available. Lebara has not raised prices since 2020 and states it has no annual price hikes — another genuinely fixed-price unlimited option, on a different network to iD and Smarty.

For pure UK unlimited, iD Mobile and giffgaff are around £10/mo cheaper and Smarty matches Lebara’s flexibility for £5/mo less. But if you regularly call abroad, adding international minutes to a big-four plan costs far more than the gap. Lebara also runs no credit check, which helps if you are new to the UK, and EU roaming is included.

O2 Unlimited Plus — £23.99/mo (24-month, offer ends 30 September 2026)

O2 Unlimited Plus is £23.99/mo on a 24-month contract (as of September 2026, source: O2), flagged as an offer that ends 30 September 2026 — re-check after that date. Every O2 plan includes O2 Priority (freebies, pre-sale tickets, retail discounts), which is the main thing O2 has that the MVNOs do not. O2’s network reaches 98% of the UK population for 4G; hotspot and tethering are included. An Unlimited Ultimate tier at £28.99/mo has higher priority.

The catch is O2’s April price rise: +£2.50/mo every year, stepping a £23.99/mo plan to about £26.49/mo from April 2027 and £28.99/mo from April 2028. At ~£24/mo before rises, O2 Unlimited Plus is noticeably more expensive than iD Mobile, giffgaff or Smarty — you are paying for O2 Priority and direct-network service. If perks do not matter, the cheaper plans do the same job.

EE Unlimited — best coverage, but the cheap version is speed-capped

EE is consistently rated the UK’s best network for coverage, particularly outside cities (source: Ofcom Connected Nations Report 2026). But be clear on what you are buying. EE’s cheapest unlimited option is a pay-as-you-go plan at around £31.50/mo (as of September 2026, source: EE via Uswitch) — and it is capped at 25Mbps, a hard always-on limit, not a congestion measure. That handles browsing, HD video and music fine, but rules out fast 4K streaming, big hotspot transfers and using the SIM as a serious home-broadband stand-in.

EE’s pay-monthly SIM contracts are not throttled like this, but they are not cheap and EE did not publish a confirmed pay-monthly unlimited price we could verify at the time of writing — treat any uncapped EE unlimited figure as “check with EE”. Pay-monthly plans carry EE’s +£1.50/mo rise every 31 March; the PAYG range has no annual rise. If coverage is your deciding factor, Honest Mobile’s ~£25/mo unlimited also runs on EE’s network with no annual rise.

Other unlimited options worth knowing

Three more, depending on your network. Asda Mobile Unlimited is ~£19/mo on a 24-month contract (as of September 2026), on Vodafone’s network with no annual price rise — the cheapest fixed-price unlimited on that network, though the app and support are basic. Vodafone Unlimited is ~£23/mo on a 24-month contract (as of September 2026), down from £35 earlier in the year, but carries the +£2.50/mo April rise. Honest Mobile Unlimited is ~£25/mo (as of September 2026) on EE’s network with no annual rise — the sensible pick if you need EE coverage without EE’s 25Mbps-capped PAYG plan, allowing for it being a smaller provider.

Best big-data SIM deals for heavy users without going unlimited

Not every heavy user needs true unlimited. If your monthly usage consistently lands between 50GB and 200GB, a defined big-data plan is often cheaper. If you use less than 50GB a month you are not really in heavy-user territory; the general SIM-only deals guide will serve you better.

Big 100GB-plus plans, ~£10 to ~£20/mo

The best big-data value sits on Three’s network. As of September 2026, iD Mobile’s 24-month plans run 110GB at ~£10/mo and 175GB at ~£12/mo with no annual price rise — at ~£12/mo for 175GB, iD undercuts its own unlimited plan by £3/mo. Smarty lists 150GB at ~£15/mo and 200GB at ~£17/mo on rolling contracts, also no price rise, with its 100GB plan currently giving 140GB for ~£12/mo. giffgaff’s 200GB goodybag at ~£20/mo (18-month) is the O2-network equivalent.

On the big networks and Vodafone’s, O2 100GB Plus is £19.99/mo on a 24-month contract (as of September 2026), an offer ending 30 September 2026, with O2 Priority perks and the +£2.50/mo April rise thereafter. Talkmobile sells 100GB for ~£9.95/mo rolling on Vodafone’s network — one of the cheapest triple-digit plans anywhere — though we could not confirm whether it applies an annual in-contract rise, so check before signing. VOXI, also on Vodafone, has a promotion until 30 September 2026: its £15/mo plan gives 140GB and its £10/mo plan gives 60GB plus unlimited social data (reverting to 25GB and 20GB after that date). VOXI is price-locked. 1pMobile’s 50GB at ~£10/mo on EE’s network, no price rise, is worth a mention for lighter heavy users.

Do “unlimited” SIM plans throttle your speed in the UK?

It depends on the network and the specific plan. “Unlimited” is not the same thing from provider to provider, and for heavy users the difference is the whole point.

Three, iD Mobile and Smarty are the most genuinely unlimited. For personal use — on-device data and tethering — there is no hard speed cap and no month-total fair-use ceiling. You can use 300GB or 500GB and your speed is not stepped down for it. The only management is deprioritisation during congestion, which is standard on every network and is not “throttling” in the sense people usually mean.

EE’s cheap unlimited is different. The ~£31.50/mo pay-as-you-go unlimited plan is hard-capped at 25Mbps — a fixed limit that applies all the time, regardless of congestion. It is genuinely unlimited on volume but not on speed. EE’s uncapped unlimited exists on its pay-monthly contracts at a higher price, so confirm which one you are buying.

O2, Vodafone and giffgaff do not apply a blanket 25Mbps-style cap on their standard unlimited plans, but fair-use and traffic-management terms vary by tier — check the plan’s own terms. In short: for uncapped speed on a big network, iD Mobile, Smarty or Three direct are the safe picks; EE’s budget unlimited is the one to watch.

Which SIM-only deal is right for you?

If you stream video and use social media heavily

Go unlimited. HD video uses roughly 3GB per hour, so 100GB disappears in about a month of daily commute-and-evening viewing. iD Mobile Unlimited at ~£15/mo (24-month, no price rise) is the best starting point; Smarty Unlimited at ~£20/mo rolling does the same job flexibly on the same network; giffgaff’s ~£14/mo promo is the cheapest if you are happy with an 18-month term on O2.

If you rely on your phone as a hotspot

You need unlimited data on a network with full tethering and no separate hotspot cap. iD Mobile, Smarty and Three all fit — all on Three’s network with uncapped speed for personal use. Avoid EE’s ~£31.50/mo PAYG unlimited here: the 25Mbps cap makes large hotspot transfers slow. If you must have EE coverage, a pay-monthly EE plan or Honest Mobile’s ~£25/mo EE-network unlimited is the better route.

If you want high data without paying for unlimited

If your usage sits between 50GB and 200GB and is fairly predictable, a big-data plan saves money. iD Mobile’s 175GB at ~£12/mo and Smarty’s 150GB at ~£15/mo are the standouts, both on Three’s network with no price rise. Talkmobile’s 100GB at ~£9.95/mo on Vodafone is the cheapest triple-digit allowance, subject to confirming its price-rise terms.

If you want to avoid mid-contract price rises

Since 17 January 2025, Ofcom has banned inflation-linked (CPI/RPI-plus) mid-contract price rises on new contracts — any rise must now be stated upfront in pounds and pence. Rises were not banned altogether. All four big networks now apply a fixed increase every spring: EE +£1.50/mo per year (31 March), O2 +£2.50/mo (April), Vodafone +£2.50/mo (1 April), and Three +£1.90/mo on 5–99GB plans or +£2.30/mo on 100GB-plus and unlimited (1 April). Providers with an explicit no-annual-rise pledge on their own pages, as of September 2026: Smarty, iD Mobile, Lebara, giffgaff, VOXI, Honest Mobile and 1pMobile, plus EE’s pay-as-you-go range.

If you travel frequently in Europe

Check roaming before committing. Three direct includes roaming in 70-plus destinations. iD Mobile includes a 30GB roaming allowance across 50 destinations. EE includes EU roaming on most plans. Lebara includes EU roaming and India roaming. VOXI includes EU roaming but the data you can use abroad may be capped below your UK allowance — check the current terms.

How to switch to SIM-only and keep your number

Keeping your existing mobile number when switching networks is straightforward in the UK. The process is regulated by Ofcom and takes one working day once the PAC code is activated.

1. Check your current contract end date — text PAC to 65075 (free, works on any UK network). You will receive your PAC code and contract end date by text within 60 seconds.
2. Compare plans and sign up — order your new SIM from the provider of your choice. Most SIMs arrive within 1–3 days. Do not cancel your existing contract yet.
3. Give the PAC code to your new provider — do this online or by phone when activating your new SIM. The switch happens on the next working day.
4. Keep your old SIM active until the switch completes — calls and texts transfer automatically. You do not need to do anything on switchover day.
5. Cancel your old contract — once your number has transferred and your new SIM is working, contact your old network to confirm cancellation. The final bill is calculated to the date of the PAC transfer.

If you do not need to keep your number, skip the PAC step entirely — just insert the new SIM and activate it on the new network.

Frequently asked questions

Written by Vaibhav Kulkarni

Vaibhav is the founder and technical editor of TheTechVector, with 15 years’ experience in quality engineering and software testing. He applies that background to auditing spec sheets, comparing price-to-performance, and checking hardware compatibility across our UK broadband, laptop, VPN, and smart home guides. All prices are checked before publication — if something’s out of date, let us know.

Prices and deals are checked before publication and marked with their source date. Mobile SIM pricing changes frequently — always verify the current rate at the provider’s website before signing up. TheTechVector earns a commission from some links on this page.