I’m not fully understanding TandemJeremy properly, so my attempt at clarification (Having just been through a similiar choice – CBT “passed” Saturday!):
You’d want to be riding a minimum 125cc scooter or motorbike for that kind of commute (I’m not sure about the 3 wheeler thingy so I won’t mention anything about that)
If you need to do a CBT, which I think you do, you’ll have 2 options to ride wither a “twist and go”/”automatic” (also called a moped or scooter) or a clutch and geared bike. Regardless of which one you do, you can ride anything up to 125cc once you’ve got the certificate, although there’s little point in doing the automatic version if you’re planning on riding a clutch and geared bike.
Once you have your CBT you can legally ride anything up to and including 125CC on L plates but not on a motorway or special road.
Your CBT is valid for 2 years, and in that time you can opt to take a test. This test can be done in one of 3 ways:
[list][*]A light Motorcycle test – which limits your riding to something below 125cc (so basically a moped)[/*]
[*]An A1 licence – Which allows you to ride something between 120 and 125cc, so a “learner motorcycle”. After 2 years it automagically upgrades itself to a full licence to ride any size bike[/*]
[*]Direct Access – You have to take your test on a bike larger than 125cc but it allows you to ride anything immediately after passing.[/*][/list]
In terms of vehicles you might want to look at, if you decide to go the automatic route, then have a look at the Honda PCX. If you wanted clutch and gears, with the idea of a larger bike (or larger automatic) down the road then have a look at the Honda CBF125.