But the rules change on January 19th and will be very different, with the introduction of new m/c and moped licences, the end of the 33 bhp class and a new A2 licence for 47 bhp bikes. What you've posted is the current rules.
The age for Direct Access rises to 24.
For the 47 bhp class you either have to have two years post test experience on a 15 bhp 125 (passing a test on that class of bike now only gives you the A1 licence) or be at least 19 (which is effectively the same thing anyway) and take a test on a 400cc bike for the 47 bhp licence. Riders with the A1 licence wil not have to take the Theory test and will take a shorter practical test. Riders without it will take tests similar to the DAS.
At 21, if you've held the A2 licence for two years you'll be able to take the short test (on a 600cc bike) for an A licence. If you haven't, you'll have to wait until you're 24 to take DAS.
If you have a full unrestricted licence, as you have, the changes won't affect you, but the point of my question was that for riders who've passed their test on a 125 and are still under the 33 bhp restriction on January 19th, then under the transitional arrangements, at the end of the two year restriction they'll (this is answering my own original question) only have an A2 licence for the 47 bhp class. They'll have to keep that licence for two years then take another test on a bike of 600cc for the full A licence.
The link to the new rules is somewhere on the .gov site. I was going to upload my MS Word copy, but the abbreviated version which I use as a reference is still 5 times the forum's maximum size limit. That document doesn't fully cover the transitional arrangements, which is why I asked the question and why I've had to do some more digging.