I am a UK citizen with a British Passport. I married a French girl and moved to France 30 years ago. Can I now renew my old UK passport and where do I go to get it renewed?I still have my old passport.
The definitive answer is available on the government web site: https://www.gov.uk/overseas-passports
This asks a number of questions. Assuming your old passport has expired, it looks like you will have to apply for a brand new passport from scratch. This may involve a passport interview. I think you can do these at your nearest UK consulate.