When you apply, you also need to send:
your birth certificate
a statement signed by you saying you’ve gone back to a previous surname (for example your maiden name) ‘for all purposes’ - that is, you will not use your married or civil partnership name at all
a document that shows you’re using your new name (for example a payslip, or a letter from your local council)
your decree absolute or final order showing both names
a marriage or civil partnership certificate showing both names - if you do not have it you can order a copy