eSIM, Home Roaming, or a UK SIM in London: What Actually Saves You Money

What your home network already covers

Start here before buying anything. Since Brexit, the UK sits outside the EU's "roam like at home" zone, so an EU-based SIM is not automatically covered for free travel to Britain, and the reverse is also true for a UK SIM travelling into the EU. The European Commission's 2022-2032 rules only guarantee free roaming among EU/EEA member states, not between the EU and the UK, so a French or German visitor should check their own operator's UK add-on rather than assume the coverage carries over.

UK networks have reintroduced roaming charges for their own customers in the EU. EE charges a 24-hour Roam like Home pass at GBP 2.50 or GBP 10 for a week, layered on top of an existing 30-day plan, while Vodafone's Zone B pass covers 47 European countries at GBP 16 for 8 days or GBP 21 for 15 days. Three's Go Roam is currently GBP 2-5 a day for customers without built-in roaming, rising to GBP 8 a day from 1 April 2026 for anyone who joined on or after 18 December 2025. None of this tells a European visitor what their own network charges to use a UK SIM abroad in reverse — that number lives on your home operator's own roaming page, and it is the first thing worth checking before you fly.

eSIM, home roaming, or a UK SIM

The three options solve different problems, not the same one. Home-network roaming keeps your existing number and WhatsApp account working exactly as at home, which matters if people need to reach you on your usual number. A UK eSIM (EE's travel eSIM, for example, runs from GBP 5 for one day to GBP 90 for 90 days) gives cheap, fast local data without touching your home SIM, but it is data-only: no UK number, no incoming SMS, though 999/112 emergency calls still work over it. A physical UK prepaid SIM is the only route to an actual UK mobile number, which some hotels, delivery apps, and UK bank verification codes still expect.

This table compares the three on the questions that usually decide it.

Where to buy a physical SIM on arrival

Heathrow, Gatwick, and other UK airports have phone-network kiosks and newsagents in the arrivals area selling prepaid SIMs from EE, Vodafone, O2, and Three, and none require proof of a UK address to activate. If you land without one, city-centre phone shops and larger supermarkets also sell prepaid starter packs, so there is no need to overpay at the first airport kiosk you see if you are heading straight into central London. Compare the data allowance against your planned length of stay: a short weekend rarely needs a 30-day bundle.

Coverage on the London Underground

This is the part that catches visitors out: mobile signal underground is a live rollout, not a finished network. As of TfL's own connectivity update, the Elizabeth line has 4G at every station and 5G in its tunnels, but on the deep Tube lines coverage is line-by-line and often limited to specific station platforms and tunnel sections rather than the whole route — for example the Victoria line currently only has signal in tunnels between Green Park and King's Cross, while the Piccadilly line has it at five central stations and between Hyde Park Corner and King's Cross. Do not plan a journey assuming you can stream a map update mid-tunnel; download offline maps for your route before you go underground.

Free Tube wifi has existed for longer than mobile signal and covers most station platforms (not the moving trains between them) for customers of the major UK networks who register once. This is a reasonable fallback for checking a message at a platform before your train arrives, even where 4G/5G has not yet reached that line.

Choosing based on your trip length

A short stopover of one or two nights rarely justifies buying and activating a new SIM at all — a short roaming pass from home, used sparingly with wifi at your accommodation, is usually simplest. A longer trip, or one where you will rely on data-heavy navigation and ride-hailing apps constantly, tends to favour an eSIM or prepaid SIM, since per-day roaming fees compound quickly over a week.

Before you land

Check your home operator's own roaming page for the UK specifically, not just their EU roaming terms, since these are frequently priced and structured differently post-Brexit. If you choose a UK eSIM, install the profile (but don't activate the plan) before you fly, so it is ready the moment you land. If you need a UK number, plan to buy a physical SIM either at the airport or in the city rather than assuming a data-only eSIM will cover every use case.