Hey sweep ... did this last week for Insurance 

You can have L plates on any bike no matter what its power output and ride it on the roads ... however if the output is more than 14.6 bhp or 11kw, you must be accompanied by a qualified instructor when out on the road for your insurance to be valid, also to be legal you must meet all the criteria for being able to ride a big bike.

JD ... your quite right for younger riders the excess doesn't alter much if at all with restriction ... however, if declared restricted & found not to be it will invalidate insurance & of course if you don restrict & should do, again it will be invalid.