In the UK the Data Protection Act means you can make a formal subject access request, you pay a fee and public bodies (incluidng the NHS) have to share their records about you with you. I think from next year, the NHS have to make medical records available on request, some GP practices already do that anyway, others you have to make a Data Protection request. As your psychiatrist has written to your GP you would therefore be able to see a copy of that letter. I'd start by asking at the GP surgery or even just by asking your GP, they often will let you read the screen they are looking at, so if they are reading your psychiatrist's letter they just turn the screen round and let you read it. You could also ask your CPN if they got a copy of the letter and if they will let you see it.