Would somebody be able to advise regarding sound proofing a wall, we only have 50mm to work with.

Laying down a good underlay on the floor but through the wall we always hear the big gobs that live there, it is not there over noisy but it keeps us awake.

Would something like these boards make that much of a difference?

http://www.keepitquiet.co.uk/quietpanel ... ofing.html

Sound Service are not cheap. The best thing you can do is put up a false wall using gypliner or richter wall lining because this will provide separation between the existing wall and the new wall. Using acoustic plasterboard will help, but the real success in acoustic work is achieving proper separation and high integrity work, making sure all the small gaps are filled or sound just exploits the weakest point.

Look at the websites for British Gypsum, Knauf and Lafarge to see what real building products can achieve at decent prices as opposed to expensive solutions marketed by sound engineers.