Unlimited data SIM deals in the UK
Last updated: 22 October 2026
Unlimited data SIMs remove the worry of running out mid-month, but the plans differ a lot in price, contract length and the small print on tethering and roaming. We list the unlimited plans we hold cheapest first so you can compare them side by side.
Compare unlimited data sim deals now →
Unlimited data SIM only plans compared
Plans our snapshot records as unlimited data, cheapest first (checked 22 October 2026). Unlimited usually comes with fair-use, tethering and roaming limits — read the block below.
| SIM | Data | Monthly price | Contract length | Runs on |
|---|---|---|---|---|
| SMARTY | Unlimited | £20.00/month | 30-day rolling | Three |
| Tesco Mobile | Unlimited | £20.00/month | 24 months | O2 |
| Sky Mobile | Unlimited | £21.00/month | 24 months | O2 |
| giffgaff | Unlimited | £25.00/month | 18 months | O2 |
| 1pMobile | Unlimited | £25.00/month | 30-day rolling | EE |
| Tesco Mobile | Unlimited | £25.00/month | 24 months | O2 |
| Vodafone | Unlimited | £26.00/month | 24 months | Vodafone |
| Tesco Mobile | Unlimited | £30.00/month | 12 months | O2 |
| VOXI | Unlimited | £35.00/month | 30-day rolling | Vodafone |
| giffgaff | Unlimited | £35.00/month | 30-day rolling | O2 |
Prices are advertised rates from each provider's own page on the date we checked, not live quotes. Clicking a name takes you to the provider.
What 'unlimited' actually means
Most unlimited UK SIMs are genuinely uncapped for normal use in the UK, but networks apply fair-use policies: very heavy users can be managed during congestion, and some plans cap speeds rather than volume.
Tethering and hotspot use is where the limits bite. Some plans allow only a set number of gigabytes of tethering each month, and a few reduce speeds after a threshold. Check the plan's own terms if you use your phone as a modem.
Roaming is rarely unlimited
Even on an unlimited plan, data used abroad is normally capped and charged under the network's roaming policy. If you travel, check the daily or monthly roaming allowance rather than assuming 'unlimited' travels with you.
Rolling plan or contract?
A 30-day rolling unlimited SIM costs more each month but you can leave whenever you like — useful if network speeds or prices change. Contract unlimited plans are cheaper per month but tie you in, and any mid-contract rise must be shown in pounds and pence when you sign up.
If you are mostly on Wi-Fi, an unlimited plan may be money wasted: our snapshot shows 20GB–40GB plans at a fraction of the price. Check your usage before you pay for infinity.
Frequently asked questions
Which network has the cheapest unlimited data SIM?
It moves with promotions. In our 22 October 2026 snapshot rolling unlimited plans start around £20 a month and contract plans a little less. Sort the table above by monthly price and confirm on the network's page.
Is unlimited data really unlimited?
For normal UK use, yes. Networks still apply fair-use management, and tethering, roaming and some streaming can be limited or charged separately — the plan's terms set the detail.
Do I need 5G for unlimited data?
No, but unlimited plans are often paired with 5G access. If 5G is not available at your addresses, check the 4G speed tier the plan gives you.
Can I use an unlimited SIM in a tablet or router?
Sometimes. Some networks restrict SIMs to phones or require a dedicated data tariff for routers and tablets. Check before putting the SIM in another device.
How do I switch to an unlimited SIM?
Text PAC to 65075 for your free switching code, then give it to the new network. Your number normally moves within one working day.
Keep comparing
Listings are dated snapshots of providers' own pages, not live prices, and CompareDirect does not sell the products we list. We are not a credit broker or lender and give no financial advice.