Internet keeps cutting out!

Hi I'm a newbie to this site and have recently had some problems with my internet. Just to set the scene my router is a BT Voyager 2110 and have one PC connected to it and two laptops using it wirelessly. My download rate is usually around 2mb.

In the last few days the internet keeps cutting out with the DSL light on the router constantly flashing. The time period of the cutting out ranges from a few mins to a few hours and is highly annoying.

I have contacted my ISP who say there is nothing wrong with the line from their end and see no problems with entrance to our house. Our telephone lines were also crackling which suggested to me that the filters were the problem, however I have changed the filters and the problems remain. In fact the download speed has reduced to a terrible 0.12mb!!

I have wasted my weekend to date, I am in the UK btw, and would appreciate if anyone could find something that I am missing. If you need any more details please ask and thanks for in help in advance!