With a few exceptions, parents in the UK can name their child anything at all. It doesn't have to be a name or even a word. People invent names all the time. In recent years, we have seen "Apple" (Gwyneth Paltrow's daughter), "Chardonnay" (lots of young girls have been named after this white wine), Fifi Trixibelle (Bob Geldof's daughter) and a whole range of other names which parents seem to choose in an effort to make their child more individual. Many of them seem to be unaware of the fact that the main result will be that people will make fun of the child because of their ridiculous name.
There is no national list of acceptable names. As I said at the beginning, there are some names which are not permitted. At the moment, I can't find the details but, for example, you can't call your child "Queen Elizabeth the Second". You are not allowed to use a first name which is also a title, as it could be assumed that you are trying to claim some kind of aristocratic title to which you are not entitled. So Mr and Mrs Smith can't name their son "Lord Smith".