When I was diagnosed didn't have any problems with my driving licence, but I was told by my consultant not to drive until I knew how my insulin reacted and I was stable... Since then no problems with renewing my licence, and no cost at all to have it renewed, you only pay for name changes and I think if your photo needs renewing..
A lot of people do however needlessly get more problems than they need due to how they answer some of the questions, by answering when asked about hypo's getting confused with what is a serious hypo, which is basically in the DVLA eye's when if a paramedic/doctor had to be called to treat your hypo, or a if a 3rd party hadn't intervened with treatment you would have landed up in A&E/paramedic called!
Apparently with the new changes to the licencing, I could if I chose apply for my HGV, and with all my data from my pump and blood glucose meter, which shows that not only do I test regularly but control is excellent and I maintain full hypo awareness I would have no problems being issued a HGV licence... Scary stuff