It does depend on your ISP customer support, I had been complaining about speeds to my ISP who just shrugged me off saying that speeds were dependant on the distance from the exchange!
I then changed ISP (O2 and I cannot recommend them highly enough) and was still having problems with erratic connection speeds and dropped connections.
A couple of hours with O2 customer support (totally free) trying different settings on the computer and router and waiting for pages to download was enough to convince them that BT needed to sort the line out.
The BT engineer came out and checked the line and confirmed that it was faulty, he changed the line to the exchange and I have been getting 6.2 download speeds since.