You must have a valid passport to enter the UK. It should be valid for the whole of your stay. You may also need a visa, depending on which country you're from. Check if you need a visa to come to the UK.

For the vast majority of international visitors in 2026, you cannot enter or stay in the UK without a valid passport. Since the post-Brexit transition ended, even EU, EEA, and Swiss citizens are generally required to use a passport to enter the country, with only very limited exceptions for those with "settled status" who may still use a national ID card. For British citizens, you do not strictly need a passport to live or move within the UK, but you will find it nearly impossible to prove your "right to work" or "right to rent" to landlords and employers without one or an equivalent proof of citizenship like a birth certificate. If you lose your passport while already inside the UK as a tourist, you must immediately report it to your embassy and the local police to obtain an "Emergency Travel Document" to remain legal and eventually leave. Without a passport or a valid immigration status linked to a digital record, you are considered an "undocumented" visitor and could face detention or deportation. The only group that can move freely between the UK and Ireland without a passport is citizens of the Common Travel Area (CTA), though they still need some form of photo ID for most commercial transport.