Stuart, hopefully you'll see this...
River conditions permitting, there are absolutely bags of perch up at Christian Malford, particularly along the Avonweir Lane section (although you'll have to put up with a large herd of curious cows...). Nothing huge, but they are plentiful and in excellent condition. Tip - lobworms are your friend.
Roach wise, I have seen, but not caught, a lot at Lacock over the bridge downstream of the Abbey. Some of these were sizeable too, but I think it's been a VERY VERY long time since a fish much over a pound and a half has come out. They are definitely there, though.
I hear Avoncliff is very good for most river species, with good average sizes (particularly chub), but chuff knows how anyone fishes it - the banks are very very steep and the few obvious swims are not that easy to get down.
There are also good roach and perch in Tockenham, and you'll find at this time of year not many people fish it. Shackells always used to have decent roach - rumours of 3lb+ fish were rife in the 90s - but I've not fished it since then, so I can't comment on the current stock. Perch were also present there, but nothing massive.
Good luck!
