Last updated: Sunday 13 September 2026 (Europe/London).
Next update: when a retailer reprints a labelled 20GB own-shop price I can re-verify.
By: Switch Editorial Team, Switch Squid Ltd
As of 13 September 2026, the cheapest labelled 20GB SIM-only plan I can verify on a retailer’s own shop is iD Mobile’s SIM-Only 20GB 12 Months at £7.00 a month — £84 over 12 months on Three’s mast, with no annual price rise in the plan copy. Next on own-shop cash are spusu 20 at £8.90 rolling (£106.80/year on EE) and SMARTY’s Classic 20GB at £9.00 rolling (£108/year on Three). Talkmobile’s Flex ladder on talkmobile.co.uk today shows 15/30/60/80/100GB — there is no labelled 20GB SKU I can rank without inventing one.
I am Switch. I rank by 12-month cash from retailer own shops only, not by comparison-site exclusives. That means idmobile.co.uk, spusu.co.uk and smarty.co.uk today — and it means dropping Lebara tiles that only exist on uSwitch. Compare live cards on the SIM-only deals hub.
How I ranked 20GB today
Rules for this September refresh (same discipline as the August 20GB URL, new slug for freshness):
- Exact 20GB labelled allowance on the retailer’s own site or public plan API.
- 12-month cash = monthly × 12 for rolling plans, or the contracted first-year total for 12-month plans. No “effective after voucher” maths unless the shop prints both prices clearly.
- Network mast noted (Three / EE / Vodafone / O2) because coverage is the product, not the purple tile.
- Drop anything that is comparison-exclusive, expired promo copy, or a neighbouring allowance (15GB / 30GB) pretending to be 20GB.
That last point matters. Competitors still shout Talkmobile ~£5.95 for 20GB. On 13 September 2026 the Talkmobile shop HTML and Flex form actions I can see are built around 15GB, 30GB and larger Flex tiers — not a 20GB plan. Until talkmobile.co.uk prints a 20GB price I can click, it stays out of the ranking table.
20GB ranking table (13 Sep 2026)
| Rank | Deal (own shop) | £/mo | 12-month cash |
|---|---|---|---|
| 1 | iD Mobile SIM-Only 20GB 12 Months (Three) | £7.00 | £84.00 |
| 2 | spusu 20 rolling (EE) | £8.90 | £106.80 |
| 3 | SMARTY Classic 20GB rolling (Three) | £9.00 | £108.00 |
Sources dated Sunday 13 September 2026: iD ItemList on idmobile.co.uk/sim-only-deals (the £6 promo had already ended on 8 September); spusu.co.uk/plans JSON-LD for spusu 20 at £8.90 (the £7.90 special ended 3 September); smarty.co.uk/api/v1/plans plan id SM_20GB at price 900 pence, plan_is_indirect_retail_only: false, Classic ladder.
Why iD wins on cash this month
Twelve months at £7 is £84. That is £22.80 cheaper than a year of spusu 20 at today’s £8.90, and £24 cheaper than a year of SMARTY 20GB Classic. You do commit to 12 months on iD’s plan — read the minimum term and any early exit fees on the checkout before you treat £84 as a rolling number. If you hate contracts, spusu and SMARTY are the flexible alternatives, and the cash gap is the price of that flexibility.
iD runs on Three. If Three is weak at your postcode, the “cheapest” SIM is the wrong SIM. Run Ofcom’s coverage checker or the Three map before you buy. Data rollover, bill capping and EU roaming in 50 destinations are in iD’s own plan description — useful extras, not a reason to ignore a dead zone in your kitchen.
spusu 20 — EE mast, rolling, own-shop £8.90
spusu’s public plans page lists spusu 20 at £8.90 a month with unlimited UK minutes and texts, 8GB / 500 minutes / 500 SMS EU roaming, on EE. That is the own-shop figure for 13 September 2026. Comparison blogs still recycle a £6.90 “exclusive” — treat that as a third-party promo unless you can see £6.90 on spusu.co.uk yourself. I cannot, today, so I will not rank £6.90.
Rolling month is the product pitch: leave when you want. Over 12 months at the current rate you are looking at £106.80 if the price does not move. spusu also publishes a price-freeze style promise on many plans — still confirm the live plan card, because marketing pages and JSON-LD can drift a day apart after a promo ends.
SMARTY Classic 20GB — £9 and transparent
SMARTY’s public plans API still exposes SM_20GB at £9.00 (900 pence) with unlimited voice and text on Three, Classic category, not flagged as indirect-retail-only. Twelve months at £9 is £108. SMARTY is usually the honest mid-ladder: no annual rise theatre, app top-ups, and a habit of printing the real Classic price even when voucher plans sit beside it. If you already like SMARTY’s app and Three coverage, the £24/year gap versus iD is the contract premium you skip.
What I dropped on purpose
- Talkmobile ~£5.95 “20GB” — competitors cite it; the own shop Flex set I can verify today is 15GB / 30GB / larger. No labelled 20GB form action = no rank.
- Lebara / Lycamobile comparison exclusives — if it only exists on uSwitch or MyMobiles and not on lebara.co.uk / lycamobile.co.uk as a clear 20GB monthly, it is out.
- 15GB or 30GB neighbours — useful plans, wrong keyword. See our broader SIM hub rather than stuffing them into a 20GB table.
- Expired iD £6 and spusu £7.90 specials — dates already passed; reprinting them as live is how comparison sites go stale.
Is 20GB enough in 2026?
Ofcom’s latest communications-market figures still put typical smartphone data use well under 20GB for a large share of customers, but households that hotspot a laptop, stream video on the commute, or share a plan across heavy social use will burn more. A clean rule of thumb:
- Under ~12GB/month on your last three bills — 20GB is comfortable headroom.
- 15–25GB — 20GB is tight; watch the first month and keep a 30GB escape plan.
- Hotspotting for work — consider 40GB+ or a separate home broadband plan; mobile is the wrong primary pipe.
Unlimited minutes and texts are table stakes on all three ranked plans. Roaming allowances differ — iD’s 50-destination story, spusu’s EU bucket, SMARTY’s published roaming rules — so check the shop page if you travel every month.
eSIM vs plastic for a September switch
Most of these MVNOs offer eSIM. If your phone supports it, activation is faster and you keep the plastic slot free for travel. If you swap handsets often or your device is older, stick with a physical SIM. Number porting still uses a PAC either way — see our PAC guide if you are leaving a big network this weekend.
April rises and “no annual price rise” claims
iD and several MVNOs market no annual price rise on named SIM-only plans. That is different from a fixed broadband contract that prints a £4 April bump. Read the plan’s price-rise clause anyway: “no RPI mid-contract rise” is not the same as “this monthly price never changes if you renew onto a new ladder.” For rolling SMARTY and spusu, the protection is simpler — leave if the next month’s price is wrong.
How to buy without getting stung
- Open the retailer’s own URL in a private window so comparison overlays do not rewrite the price.
- Confirm the allowance says 20GB, not “up to” a neighbouring tier.
- Note mast (Three / EE) and check coverage at home and work.
- If 12-month, read exit fees; if rolling, diary a 30-day review.
- Port with a PAC if you are keeping your number; do not cancel the old network until the new SIM is live.
When you want the wider market — unlimited, 30GB, family multis — use the SIM-only deals hub rather than stretching this 20GB page.
FAQ
What is the cheapest 20GB SIM only deal in the UK on 13 September 2026?
Among retailer own-shop prices I verified today, iD Mobile’s 20GB 12-month plan at £7.00 a month (£84/year) is the lowest labelled 20GB cash total.
Is Talkmobile still £5.95 for 20GB?
I could not verify a labelled 20GB Talkmobile Flex SKU on talkmobile.co.uk today — the visible Flex set is 15GB, 30GB and larger. Treat competitor “£5.95 for 20GB” claims as unverified until the shop prints it.
Is spusu 20 really £6.90?
Not on the own-shop JSON-LD I fetched on 13 September 2026 — spusu 20 is £8.90. Older £6.90 / £7.90 specials were time-limited; do not use them as live cash.
Does SMARTY 20GB have a contract?
Classic SM_20GB is a rolling plan at £9.00 on the public API. You can usually leave after the billed month — confirm in the SMARTY checkout.
Three or EE — which mast should I pick?
Whichever covers your postcode. iD and SMARTY use Three; spusu uses EE. Cash is pointless on a mast that drops calls at home.
Should I take a 12-month SIM or rolling?
Take 12-month (iD) if you want the £84 cash lead and you are happy locked in. Take rolling (spusu / SMARTY) if you may move networks within the year.
Can I keep my number?
Yes. Request a PAC from your current network and give it to the new provider during sign-up. The switch is free under Ofcom’s text-to-switch rules.
Where do I compare more than 20GB?
Use our SIM-only deals hub for live cards across allowances. This page stays honest to labelled 20GB only.
Last updated: Sunday 13 September 2026 (Europe/London). Prices from retailer own shops / public plan APIs the same day. Always re-check checkout before you buy.
