I think the whole internet is slow and every time some clown improves my speed it seems to only have an effect for a couple of days and then reverts back again. I do wonder one day if the whole thing will just go pop, that would be interesting!
ISP's are buggers for reducing your line speed without telling you. I can't speak for all of them but BT have a speed checker which literally takes a couple of minutes to do. You just need to go to their broadband speed page, connect your laptop to your hub with a ethernet cable and click on 'test'. I haven't had any issues for months now mind you.