You need a passport to travel outside of the UK and return home. However, what happens when your passport is damaged when you get caught in a rainstorm, it goes through the wash or falls into the swimming pool? These events aren't uncommon and do not present an insurmountable problem.
Damaged passport validity
Damaged passports usually aren't valid to use, but different countries and border control staff handle these problems on an individual basis. The risk of being inconvenienced by a denied passport is great, however. Replace your damaged passport as soon as possible. Even though the passport may still be readable and can be scanned, airlines and border control staff reserve the right to refuse to accept a damaged passport.
Damaged passport replacement
Her Majesty's Passport Office (HMPO) will provide detailed information on getting a new passport. While in the UK, you can also visit your local Post Office to learn how you can get a new passport and pick up the forms necessary for renewing your damaged passport.
Damaged passport abroad
If you are abroad and your passport is damaged, go immediately to the nearest UK embassy or consulate. If these offices are not available, you might get assistance from an allied country's embassy or consulate. In some cities, you may be able to receive assistance at the main airport.