Nothing in law requires it#
Converting to a religion changes nothing about your legal name. No UK law, and no religious body, issues or requires a new name, and GOV.UK's deed poll guidance asks for no reason for a change of name at all. People who take a new name on conversion do so as a matter of faith, tradition or preference, and the law treats it like any other choice: the new name is yours from the moment you adopt it and start using it, and a deed poll is the document that proves it to the organisations that hold your records.
If you choose a new name#
You can change as much or as little as you like. GOV.UK says a deed poll can change any part of your name, add or remove names, or change the spelling, so a new first name with your family surname kept, an added name, or an entirely new name are all one deed poll each. The rules are only about the name itself: it must be pronounceable, it cannot include symbols, numbers or punctuation apart from a hyphen or an established form like O'Hara, it cannot be offensive, and it cannot be a title.
If the name comes from a script other than the Latin alphabet, settle on one spelling before you sign, and use exactly that spelling on the deed and everywhere afterwards. A passport, a bank card and a driving licence that spell the same name three ways will each be treated as a different name by the computer systems behind them.
What organisations check#
The reason is not among the things any organisation asks about. What they check is the deed, and for a passport GOV.UK's guidance says to send the deed poll with evidence that you are using the new name, such as a payslip or a letter from your council. The Home Office's guidance on the use and change of names adds one point of routine that is worth knowing rather than worrying about: when a change of name is made for a purpose other than marriage, adoption or a change of gender, both the previous and the acquired names may be checked against police and other records. That is a check for fraud, applied to every change of this kind, and it is not a judgement on the reason.
If you are not a British citizen#
The deed poll works for UK organisations whatever your nationality, but the Home Office expects the name on an eVisa to match the name on your passport or national identity card. If you are changing your name on conversion and you hold a foreign passport, the guide to changing your name if you are not a British citizen explains the order to do things in.
