The only site which review builders, etc, seem to be open for abuse by the companies which are being reviewed, i.e. by submitting their own recommendations. So I was a bit sceptical when I read these:
http://www.freeindex....atories%29_283605.htm
However it looks as if the company has simply copied (apparently genuine) comments from their customers, which can be viewed by clicking on the forms shown here:
http://www.allstyle-windows.co.uk/reviews.aspx
I'd recommend asking to see the originals of those forms (where the addresses haven't been obscured) and checking with their customers about the validity of those comments. (Possibly even call round to take a look at the conservatories!). If they're as genuine as they appear to be you might want to consider that firm's services.
So I'm certainly not actually recommending that company (which is fairly close to you) but it might well be a good starting point. (Incidentally I've searched the web for anyone criticising that company and I've not found anything).
Chris