Dear LustForLife-- your story makes me feel really quite angry. And it almost happened to me ...
My GP practice was offering 'health checks', so I went in for one last month. They took blood for routine testing, and also weighed and measured me-- I had unintentionally shrunk from BMI 18.5 (normal for me) to 16.
The head GP, Dr L, rang about 5 days later-- in the evening, while I was standing in the supermarket!-- and bluntly told me "your blood test results have come back, and you have diabetes." He started to say something about HbA1c, but I told him I wasn't in a position to discuss this now, and as it happened I had an appointment about something else with one of the other GPs, Dr M, the following morning; I would discuss it with her.
This meant I had the time, before speaking to Dr M, to look up information on diagnosis of Type 1 diabetes and Type 2 diabetes-- in particular the NICE guidelines:
https://cks.nice.org.uk/topics/diabetes-type-1/diagnosis/diagnosis-adults/ on the one hand and
https://cks.nice.org.uk/topics/diabetes-type-2/diagnosis/diagnosis-in-adults/ and
https://cks.nice.org.uk/topics/diabetes-type-2/background-information/risk-factors/ on the other.
So when Dr M told me my HbA1c result was 101 (with 48+ meaning diabetes), I asked her whether she thought it was Type 1 or Type 2; she immediately said "Type 2"; I asked why, she immediately said "Because of your age"-- and I said 'But the NICE guidelines say "Do not discount a diagnosis of type 1 diabetes" simply because of the patient's age' ...
She ignored this at first and just went on about prescribing me Metformin! But I kept saying 'I really really don't think I have Type 2' and pointed out that that, according to the NICE guidelines, I had none of the risk factors for Type 2 but ticked three of the boxes for Type 1.
Eventually-- I think to get rid of me!-- Dr M suggested I have an appointment with the practice diabetes nurse. I said yes please, and could it be as soon as possible. Dr M said she'd speak to the nurse and get back to me.
When Dr M rang back-- my guess is that she had spoken to the nurse and the nurse had set her straight! She said she had now e-mailed the hospital diabetes unit for urgent advice; one of the hospital diabetes specialist nurses rang me a couple of hours later and asked some questions and then told me to come in to see them asap, the same day if possible, if not, the following morning. Went to see them and was diagnosed with probable T1D (since then confirmed by C-peptide and autoantibody tests) and immediately started on insulin.
If I hadn't looked up the NICE guidelines-- I might simply have accepted what Dr M said and taken the Metformin-- and god only knows what would have happened.
Admittedly, my case is more extreme than yours: you said above you're "6.2"-- 6 foot 2?-- and "was 12 and a half stone, now 10 and a half and falling", which would mean (I just used an online calculator) your BMI was 22.4 and is now 18.8. So you're still (barely) within the healthy BMI range. But-- it is a significant unintended weight loss, and that plus the fact that even at the outset your BMI was under 25, plus the fact that the pills aren't working, means you should get a
swift referral to a diabetes specialist unit.
So-- do follow rebrascora's and Windy's advice-- try the DUK helpline, and be "politely pushy and persistent" with your GP! All the best, and hope you get proper treatment soon.
PS I too have huge respect for the NHS, and understand how overstretched and understaffed and underfunded they are. What makes me angry is not so much Dr M as a system in which GPs don't have the time to stop and think and make use of resources created specifically for them, like NICE's Clinical Knowledge Summaries ...