Does anyone know how much it costs roughly to adjust clearance valves on kawasaki gt550 with 9700miles on the clock? I live in the bristol area.

Yeah, it costs nothing if you do it yourself.
Have fun

Measure the clearances first, if you haven't already, it's fairly easy.If they need adjusting, you'll be looking at 250+ dollars, don't know what that is in Euro.
Buy a manual and do it yourself!
Don't be dependent on a dealer!
Think what a nice Kawi jacket that money could buy...
Lots of tech help available here if you decide to try it.