Well first off before you can even get your L-plates you need to do a CBT (Compulsory Basic Training) which allows you to ride up to a 125 with less than so much hp (I think about 15) on L-plates on the roads, but you aren't allowed to go on motorways or carry a passenger and some other stuff.
Then you need to take a theory test which allows you to take the practical test
You then take a module 1 test which is off-road in a test center (which some people have to ride for hours to get to because they didn't build enough) which makes you drive through cones in a slalom and do emergency stops and the like.
If you pass that then you take the module 2 test which is on-road just riding around like a driving test.
If you are 16 you can only ride up to a 50cc scooter with a speed limit of 28 mph (pretty dangerous).
If you are 17+ you can get a full license but have to restrict your bike to 33 bhp for 2 years after passing.
If you are 21+ you can take your mod1+2 on a bike with 50bhp+ and then you are unrestricted after passing, but if you do your test on a 125 you are still restricted.
I have to go back to university next week and couldn't get a mod 2 test in time, so will have to do that at christmas.
Electric bikes based off batteries are again no good because the batteries are so heavy.