Anybody over the age of 16 may change their name and call themselves more or less anything they like. There is no need to pay a lawyer or for any formality. Just insist that people call you by your chosen name. The only restriction is that any change of name must not be with an intention of misleading or defrauding anybody by using the new name.
Some institutions such as banks and government agencies however may call for proof of your new name. For certain purposes where there has been a change of name, such as to obtain a driving license or passport in the new name, evidence is required by way of a Change of Name Deed [or deed poll], or a Statutory Declaration.
If you have been using a new name without completing a Change of Name Deed you may be called upon to provide a Statutory Declaration. This could be called for by a bank, or government department, or official body.
A Statutory Declaration is a more official document, and must be sworn before a solicitor, magistrate, or authorised Officer of the Court.
It is also possible to change a child’s name by a Change of Name Deed. However all parents who have parental responsibility must consent to the change of name, as must the child if he/she is aged over 16. If this consent is not forthcoming, it will be necessary to apply to the Court by way of an application for a specific issues order for permission to change the name.