If the Belkin does not give the diagnostic info that the guys here need to help you, it might be worth considering using the BT Home Hub for a few days whilst things get resolved?
I've reverted back to the Homehub 2.0 and its at a solid 7mb now!! issue with the belkin,
Thank you for your help though 🙂
I never did get on with Belkin equipment myself, but that's just me being biased and un-scientific