Threre are a number of hood cleaners around, you should be able to find something in Halfords or somewhere similar, just make sure that you apply some kind of protectant after you've washed it as the cleaners may remove some of the protectant applied during manufacture.
Everyone here advises a product called 303 (do a search in this forum, it's kinda like Scotchguard for exterior vinyl/fabric). It appears to be a US product but I managed with a litttle effort to find it in Australia so I'm pretty certain you'll find it in Blighty.
When I clean my car I tend to vacuum the hood, it may sound a bit strange but this was the advice on the 303 product. Not sure if it works but I do it anyway
