If a person wishes to be known by a different name they are entitled to change their name at any time. They can change their forename and/or surname, add names or rearrange their existing names. In Scotland there is no set legal procedure that they must follow in order to change a name. They can simply start using the new name.
Transsexual people usually permanently change their name once they have reached the stage in their transition where they are living full-time as the gender which matches their gender identity (i.e. the opposite gender to that which they were labelled at birth). This is often before they have started hormone treatment or had any surgery.
Some other transgender people who do not intend to transition might also permanently change their name, often to a gender neutral androgynous name. Alternatively, they may use a different name just among friends – in a similar way as the many non-trans people who use a shortened version of a longer name among friends. It is perfectly legal for any transgender person to use two different names (as long as they are not doing so to defraud anyone) and to have some documents in each name.
There are some circumstances, such as applying for a passport or getting a bank account switched into their new name, when written evidence of the change of name is likely to be required. This evidence could take the form of a letter from a professional person (for example their doctor), a statutory declaration or a deed poll. The easiest and cheapest method is a statutory declaration (see below for an example). A practising solicitor, notary public, or other officer of a court authorised by law to administer an oath, needs to witness them signing it. They should also ask the solicitor or notary public to make several certified photocopies for them. The cost should be less than ten pounds.