belgium is cheaper than france, germany and the netherlands
germany is actually quite expensive fwiw. luxembourg is the cheapest in western europe, as they have rather low fuel, alcohol and tobacco duties
however, with the pound worth naff all, ymmv.
probably doesn't concern you, but the cheapest diesel is in belgium and the luxembourg (obv)
filled up on friday @ 90cents/litre i think petrol was around €1.20
motorways are always 10-15% more expensive than petrols stations on A and B roads, and unmanned ones are 1 or 2cents cheaper than ones with a shop.