Can I use my old passport after changing my name?

An expiry date in the future does not, by itself, prove a passport is usable. A document can have been cancelled before its printed expiry date.

GOV.UK’s general passport guidance says a name change requires a replacement passport for travel or identity use. The published marriage guidance is more specific. If you have signed a deed poll, ask HM Passport Office about your actual circumstances instead of assuming that the marriage exception applies. GOV.UK: passport name changes

Explain whether you have already applied for a replacement, whether the old document is with the Passport Office and whether you have booked travel. Do not state that a deed poll instantly cancels every passport, or that every unexpired passport is necessarily safe to use. Both shortcuts hide the important details.

Keep a cancelled passport if an authority tells you it is needed as supporting evidence for an existing visa, but do not confuse carrying it with travelling on it. Ask the visa issuer what must accompany the new passport and whether a name change affects the permission.

For a bank, employer or other identity check, ask what combination of documents it accepts. A passport in a former name may need additional linking evidence, and its acceptance for one administrative purpose does not establish its validity for travel.