Tried unplugging and re plugging the router in, improved my sky speed a lot the other month.
Also, dont ring sky, email them, they take a stupid amount of time to reply but when they do they usually sort it. I have managed to get them to put me on a fixed speed of 2.5mbps, which i do get compared to when i was on the upto 8 when i was lucky to get 1.5mbps.