If you are a British or Irish citizen traveling from the UK mainland to Jersey by ferry, you do not strictly need a passport, but you are required to carry some form of valid photographic identification. Because Jersey is part of the Common Travel Area (CTA), there are no routine border controls for domestic travelers. Accepted forms of ID typically include a driving license, a national ID card, an expired passport (if it's within two years of expiry), or even a bus pass or student ID, depending on the ferry operator's specific security policy (like Condor Ferries). However, if you are not a British or Irish citizen, or if you are arriving from outside the CTA, a valid passport is mandatory. It is always a good idea to bring a passport if you have one, as it is the most universally accepted document and ensures a smooth process if your ferry is diverted or if you need to prove your identity to local authorities.