You must fill out the application for a direct airside transit visa to change flights in the United Kingdom and not be taken through the border control. This means that if you have your connecting flight within that day as the one where you landed, you need a direct airside transit visa.

Whether you need a Direct Airside Transit Visa (DATV) for a layover in London depends on your nationality and whether you need to clear UK border control. If you are from a country that generally requires a visa for the UK (such as India, Pakistan, or many African nations), you typically need a DATV even if you do not leave the airport's "International Transit Zone." However, there are many "Exemptions" to this rule. For example, if you hold a valid visa or residence permit for the USA, Canada, Australia, New Zealand, or a Schengen country, you can often transit through the UK without a visa. If your layover involves a "Landside" transit—meaning you have to collect your luggage, change airports (e.g., from Heathrow to Gatwick), or stay overnight in a hotel outside the terminal—you will likely need a Visitor in Transit visa unless you qualify for the "Transit Without Visa" (TWOV) concession. In 2026, with the full implementation of the UK ETA (Electronic Travel Authorisation), many travelers who previously didn't need a visa must now have a valid ETA even for a short transit. Always check the official UK government's "Check if you need a UK visa" tool before booking your flight.