It used to be out of the question, but since the rules changed last year, and you can now apply for a HGV/bus licence then it's possible. First I check out the DVLA website, as it will give you the details what form you need etc, I think it's something like a D4!
But the jest of it all, is that you have to prove your diabetes is under suitable control, by providing specialist reports and blood glucose monitoring data etc.. Then if I remember rightly you will have to go through a yearly medical to keep the licence..
But it's one thing to obtain the correct licence but another totally different matter getting an employer to employ you, but this is like many jobs though,,, My hubby trade is actually brick layer, and in his time he was a very accomplished and in demand bricklayer.. But he was self-employed, taking on private and sub-contracting jobs, but back in the 90's when the building industry stalled, he took a career change purely because when he tried to return to be taken onto a company's books... He found that yes they were more than willing to sub-contract to him, but due to his diabetes that weren't willing to take him on... So after 6 months of virtually no work coming in, he jack it all in and changed his career.