All been said I think. Major roads in the UK aren't too bad, but local roads and town roads once you hit the city limits can be awful. Entering Oxford city from the London road used to be hair-raising until last year - for a stretch the road surface was so bad it could shake your hands off the bars! (has been fixed now though). And be very wary if you leave major roads at night - some villages can be so totally blacked out at night you'd think you're back in wartime. No road or street lighting, no road markings, cars parked on the edge of the road without lights - e.g. this is the village of Tetsworth in Oxfordshire, where you take your life in your hands on two wheels at night.
There is the equivalent of vehicle road tax in Belgium, at least on cars. But it's all done on the database - UK is the same now.