I am not an expert but as far as I can recall you cant drive on the motorway with L plates at all. The fact that you have a full car licenice does not change this. Also the A2 test restricts you to riding a machine of 33bhp or under. When you pass your A2 test, you will be able to ride a bike of any cc, as long as it is restricted to a 33bhp. Motorcycles that are normally over 33bhp can be restricted, but you will be required to have a certificate of restriction.
hope that helps