If your car is legal registrated and insured in the UK....nothing have to be changed.
The only item I see is the headlights as these are directional.There is a trangular shaped sticker to be put on the lenses to not blind the upcoming traffic.
For your own safety you can add some blinkers. A fire extiguisser, a triangular a first aid kit and fluo jacket for every person in the car is needed.
That is all for Belgium. For france I think it is the same, For germany you need to add some latex handgloves for the first aid kit.
For wintery conditions you need wintertires in germany. If you do not have them....you get a fee for each tire and they can send you to the nearest tirecenter.
Btw: Hessich Oldendorf is in June 2009, next Bad Camberg probably in june 2011.
Greetings.
ZELENSIS, coachbuilt body from the 50's on a vw platform made in Belgium. Peter the heb detective