Using an eSIM in London

What London is like on a phone

London mixes first-time visitors and daily commuters in the same carriage, and both live off the same screen. Most leisure trips here run to a tight shape — museum in the morning, market at midday, a theatre barcode in the evening — and every one of those steps is booked or shown on a phone. Above ground the signal is rarely the problem, even where tall buildings crowd together. The character of the network here is simple: strong upstairs, intermittent downstairs.

When you land

People land at Heathrow (LHR), Gatwick (LGW), Stansted (STN), Luton (LTN) or London City (LCY), and anyone coming from Paris or Brussels steps off Eurostar at St Pancras instead. Switch the line on in your seat after landing, or in the arrivals hall at the latest, because the moment you walk out you have to choose between an express train, the Elizabeth line and the Piccadilly line. The ride in from Heathrow alternates between covered tunnel sections that go quiet and open stretches where the bars come straight back. Coming in by Eurostar you have service from the moment you step onto the platform.

Where coverage changes

Above ground London has almost no dead spots: the glass canyons of the financial district, the Thames walkways and the big parks all stay usable. The real change is underground, where tunnel coverage has been fitted line by line and is not finished, so one line talks the whole way and the next goes silent until the following station. The Elizabeth line and many main-line platforms tend to hold up better than the old deep-bored tubes. Basement pubs, galleries built below street level and the lifts in older buildings are where the signal drops without warning.

What a day here costs in data

A normal walking day in London runs about 900MB to 1.5GB, most of it going to a map left open and a transit app re-checked before every boarding. Booking a museum slot or collecting a theatre ticket costs little each time but happens all day. If you plan to upload clips from Borough Market or stream music on the top deck of a bus, allow roughly another half a gigabyte. Travellers who rarely need translation here use less than they would in a city where every sign has to be photographed.

Districts travellers ask about

• Westminster and the South Bank — You can walk both banks without losing service, though when the crowd thickens around the London Eye and Parliament at dusk, heavy images take noticeably longer to load.
• The City and Shoreditch — The financial streets hold up through the working day, but the narrow old lanes between towers and the basement bars of Shoreditch are where the line drops most often around here.
• Kensington and the museum quarter — The avenues around the museums are fine, but galleries set deep behind thick walls and on the lowest floors often leave you with the building's own Wi-Fi and nothing else.
• King's Cross and Camden — Around King's Cross and St Pancras you get some of the steadiest service in the city; at Camden Market on a weekend the crush is thick enough that an app payment can take a few seconds to go through.

Day trips out of the city

• Windsor — Trains from Paddington or Waterloo are short and hold signal nearly the whole way; inside the castle's very thick walls is the one place worth having your ticket already loaded.
• Oxford — The line runs through open country with steady service; once you are in town, the stone quads and cloisters ringed by high walls knock the speed down in patches.
• Brighton — The line south dips through cuttings and short tunnels that make the connection stutter, then the seafront and the pier give you full service again and plenty of room to upload photos.