asked Her Majesty's Government:

Whether a United Kingdom passport holder who has changed his or her name may continue to use the passport in his or her previous name. [HL1739]

As stated in my reply of 19 January 2007 to a previous Question, there is no legal obligation for a person who has changed their name to surrender their existing passport until they apply for a replacement. However, airlines and other international passenger carriers would be unlikely to allow boarding where a name in a person's passport differed from that on their ticket.