Recently diagnosed T1 so went onto insulin in July.
I had to notify DVLA; still able to drive (I rang and checked) after sending in form while they processed it. Had to send in license and got a three-year one a week later.
Had to notify insurance companies (Wife and mine); chat went something like:
Me: "I've just been diagnosed with a DVLA reportable condition, T1 Diabetes that will be insulin-controlled. I need to notify you."
Insurance Company: "OK. Couple of questions, has a doctor told you not to drive?"
Me: "No."
Insurance Co: "Has the DVLA told you not to drive?"
Me: "No."
Insurance Co: "OK. That's it. Updated."
Me: "Is that it?"
Insurance Co: "That's it."
Me: "No change in premiums?"
Insurance Co: "No change."
Basically, as long as the DVLA tell them I'm safe to drive, they're can't contradict.
I do find that driving lowers my blood sugars so I keep my spare monitor in the car, and there is several packets of mini jelly babies in the glove box, one of them open. I operate on a strict Jelly Baby per 15-20 minutes of driving. On longer journeys, I also stop off at a service station, get a medium latte and have that unbolused. In addition, if I am driving I always run my sugars a little bit higher before getting in the car by putting 10% less insulin through for my previous meal. It raises it from 4.5-5.5 to 5.5-6.5.
As for when I started driving post-diagnosis, I did very short journeys - to supermarket and around town - for the first week until I worked out my sugars and how I felt. My first hypo was actually when I was driving (and the only one I've had while in the car to date). I went down to 3.9. I was starting to feel funny, pulled over and tested. And then had an hour to kill looking 'round the shops until I could drive again!
And ... test before you get in a car and 2hrs into any journey. Take fast-acting carbs if you are below 5.0, don't drive if you are below 4.0. If I am hypo, I like to stay in the permitted zone for 30-45 minutes before taking control of the vehicle.
Hope this helps,
John