Microlight clubs and schools in the East of England. (I've yet to meet a poor microlight school, so I'd suggest going to have a look at the 2 or 3 nearest your home and picking on you like. There are loads of threads you can search out on picking a good flying school.)
For the diabetes, have a look at
this document which at page 31 shows a table that should allow yourself to categorise yourself as group 1 or group 2. (You're probably familiar with it already.)
From the NPPL website:
The medical standards are based on the DVLA driving medical standards. If there is nothing in your medical history which would stop you reaching a DVLA Group 2 standard for professional driving, you can obtain a National PPL without any medical limitations. If you have a past history of significant illness but meet the Group 1 standard for private driving, you will only be able to fly either solo or with another “safety” pilot qualified on your aircraft type. A pilot acting as a safety pilot must be appropriately briefed. Other limitations may be imposed on individual pilots depending on the advice received from a Medical Adviser. Your GP’s countersignature is to confirm the lack of any medical history which would preclude you meeting the appropriate DVLA standard. Your GP is entitled to charge you for this service.
So almost certainly the worst you'll face is being unable to fly with a passenger who isn't a pilot, but there's a good chance you won't even have that restriction if you've had no incidences of hypoglycaemia in the last year.
And you are quite right, microlighting is tremendous fun.
G