I did my mum's by filing in the downloadable forms and getting them signed by appropriate people and sent off.
Not so easy in Scotland, where Marionq and Cherryade are. The Scottish lawyers have been crafty, there are no downloadable forms, and from what I found on a google it is stonrly pointed to go to a Solicitor although Katrine did direct me as to how to do it oneself. The whole document has to be drawn up. Having said that the solicitor my MIL uses produced what I considered a defective version the first time round, and we had a battle to get her to add replacement attorneys, but that is another story.