https://en.m.wikipedia.org/wiki/Name_change
"...In theory anyone who is at least 16 and resident in the United Kingdom can call themselves whatever they wish. However, over the past hundred years or so, formal procedures that are recognized by record holders such as government departments, companies and organizations have evolved, which enable a citizen legally to change the name recorded on their passport, driving licence, tax and National Insurance records, bank and credit cards, etc., provided that "documentary evidence" of a change of name is provided. Documents such as birth, marriage and educational certificates cannot be changed because these documents are "matters of fact", which means that they were correct at the time they were issued...."
It is fraud unless there is documentary evidence.