To check in at a UK airport in 2026, the requirements depend on your destination. For international flights, a valid passport is mandatory for all travelers, and you must ensure it meets the "validity" rules of your destination (often requiring 3–6 months of remaining life). You may also need to present a visa or an Electronic Travel Authorisation (ETA) depending on your nationality. For domestic flights within the UK, requirements have become stricter: major airlines like British Airways now require valid photographic ID for all adult passengers. Accepted forms typically include a passport (even one expired for up to five years for some carriers), a full or provisional photo driving license, or a national ID card. While children under 16 often don't need ID if traveling with an adult on domestic routes, it is vital to check your specific airline's policy, as some now require ID for everyone to comply with enhanced security vetting protocols.