I think you can ride a 125 on a provisional licence for two years once you've done CBT. I'd get a 125, ride it around on a provisional until you're 21, then do a direct access. If you need to go on motorways or carry a pillion though, then take your test. I rode about for a year on an AR50, then did a one day intensive course on a CG125 and passed my test first time. Only cost me about £160 all in including hiring a bike for the test, although that was 6 1/2 years ago. I haven't riden a bike since (not for more than 5 minutes anyway), but I've been entitled to ride a superbike since I was 19 1/2 thanks to the government's krappy 2 year rule. Idiots
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Rich :¬)