Hi witsum,
As I said before, pre-diabetes is technically classed as a condition. Diabetes is classed as a chronic condition. It doesn't matter what kind of a condition it is, you still need to advise the insurers. When they give you a quote just make sure that they will meet any claim you might make in respect of that condition. Don't assume that because they have given you a quote that they are covering you for all the things you have told them.
Let me give you an example. Last year my annual travel policy came up for renewal. I had insured with the company (a household name) for many years as a diabetic. But the renewal details said (in tiny print), that they will no longer provide cover for any condition that already exists (i.e. my diabetes) despite them having covered it every year in the past. I tried several other insurers and each one asked about medical conditions, and I told them. In each case the insurer gave me a quote, but it was only when I specifically asked whether the diabetes was covered they all said no.