Once a UK passport has expired, it is no longer a valid travel document, but it still holds significant value as a foundational identity document. When you apply for a renewal, HM Passport Office typically requires you to send in the old one; they will cancel it by cutting off the corner of the cover and then return it to you (if requested). You should keep this cancelled passport in a secure place. It can be useful for proving your identity for historical purposes, such as verifying your name changes or helping with citizenship applications for your children. In some cases, a recently expired passport (usually within 6 months to a year) may still be accepted by some UK banks or employers as secondary proof of identity, though a valid one is always preferred. You should never throw an expired passport in the bin, as it contains sensitive biometric data and personal information that could be used for identity theft. If you truly want to get rid of it, you should use a secure document shredding service or return it to the passport office for secure disposal.