I have just done this. Passed on wednesday.

Book and do your CBT. It will be on a 125 and will cost about £100

Then book and do your theory test. Make sure you book a motorcycle one as it different to the car one. About £40

Once passed go see an instructor. You can either do a DAS course or just have lessons and spread the cost like i did.

I had 3 hours of lessons for the MOD 1 then took the MOD 1 test and passed. Takes about 10 mins to do.

link to MOD 1 video
http://www.youtube.com/watch?v=ZwYsMajnlRY

Then had 4 hours riding on the roads. this wasnt to learn how to ride it was to get me out of bad habbits. you will be surprised at how many shoulder checks, mirror checks life saver checks you have to do, and how easy it is to forget them.

Then went for the MOD 2. this is £75 + bike hire so £50 on top of that.

All together cost me just under £500 and took bout 4 weeks.

CBT is on a 125 then all the lessons and both parts of tests are done a Honda CB500.

If you do your test on the 500 you can ride anything you want when you pass no restrictions at all except insurance.

Pass on a 125 and your stuck with 33bhp for 2 years.

Just a note if you do a 3-4 day course. the MOD1 and MOD2 will be on the same day. if you fail the MOD 1 you can't take the MOD 2 so £75 down the shitter.

Also the instructor will have pre-booked tests so they will just put your name to the test no need to book these your self you just pay the instructor.