Diagnosed with Type 2 Diabetes for 12 years and did not notify my car insurance until the end of July this year, when up for renewal. Reading an article on Diabetes UK, it said to inform the insurer when diagnosed. I was renewing with Direct Line and called their customer support number. Apparently, I did not need to inform them. If my GP and the DVLA are happy for me to drive, that is fine with them, the lady even checked with her supervisor. (If your GP or the DVLA were not happy, you would not get motor insurance any way). I did record the date and time, who I spoke with and what I was told, should it be required in the future. I suppose the best thing is to tell your insurer when diagnosed. If there is any issue, consider moving insurer. And keep a record of any conversations!