For a relatively small amount of money they give you the document you need worded exactly as it needs to be and also include instructions on effecting it and how to use it with HM Passport Office (they ask you do NOT send a covering letter with it, just the evidence of your new name being in use). I got several copies done for a little extra more, so I have them for future plans. Fast service. You could find everything you need on the internet, but with so much misinformation out there it was a small price to pay to know I'd be getting it right first time. Thank you all.