I have never liked my first name. I understand that from day-to-day I can call myself by a different name but that I cannot change my surname. Can I legally sign to this new first name?
You can choose your first name, and indeed your surname, more or less as you like as long as you are an adult and your motive isn’t fraudulent. If you are asked for a formal proof of your identity you may have to produce one of three documents: a note from a respected member of the community confirming that the new name is the one by which you are commonly known; a sworn statement, prepared by a solicitor; or a change of name deed, which is similar and is the most formal method of regularising the change. But you shouldn’t need any of these just to alter your first name.