Professor Andrew Hattersley of The Peninsula School of Medicine and Dentistry in Exeter, developed a home urine test for C-peptide around 2011 (C-peptide results and insulin results will be the same). Dr Rachel Besser used it on 300 people in a Diabetes UK funded study more recently.
Not only does it show the difference between endogenous and exogenous insulin, it can differentiate between Type 1 and 2 and has been used to get misdiagnosed patients with MODY off insulin altogether. BUT not only can I not find it for sale, many people seem not to have heard of it.
Potentially it could be showing Type 1s how much insulin they make, if any, so it can be allowed for. It should be available by now so that no-one is wondering am I 1, 1.5, 2 or MODY ? One MODY patient who had been misdiagnosed was on insulin for 11 years when she didn't need it.
I think the NHS needs to use tests to show which type patients have and how much insulin they produce, as a starting point.