Is the problem that the link has been truncated when it became a clickable link? What happens when you click on that link? You should be getting the New Posts page still but without The Tea Room (forum # 44) and Poetry (forum # 45).
So if you just want to exclude Poetry it would be
http://forum.alzheimers.org.uk/search.php?do=getnew&exclude=45
And this is the original one
http://forum.alzheimers.org.uk/search.php?do=getnew&exclude=44,45
Hopefully neither of those are clickable links so you can see the entire string.