Sorry to picky but in UK one can choose to use almost any name one wishes, as long as the intention is not criminal. (Cannot use a name which infers a title, e.g. Lord Smith)
Any name, maybe a maiden name or it maybe any name at all. Thus if I want to call myself 'Freeda Knowitall' I can. I can then change every document and my record with everyone (bank, passport, D/L, DWP, etc) with the ONLY exception of my Birth Certificate, on which the name cannot be changed.
To do this one can choose, Deed Poll, a Statutory Declaration (on oath before a magistrate) or by Common Law (no legal formalities at all).
All methods are equally 'legal' although in UK there is no law which says a person can change their name (even on marriage) but there is also no law which says one cannot. Thus it not strictly legal but it is not unlawful.
In practice this mean anyone can change their name for all purposes. I did so about 25 years ago.
(If you want to say I am wrong, thats fine but please quote a legal source for reasoning)