Thanks guys for your input and information, it will be interesting to see how the rest of the tyre scrubs off! In all the Bm’s I have owned none of them have worn the front down so quickly. They are taking the measurement straight from the middle of the tyre, away from the sides. I have used my digital vernier ( calibrated!) and I cant get any lower than 3mm. I am a “butterfly” and only go out in the sun on this bike, am fully aware of the consequences of riding on worn tyres and wont take that risk…even in the dry.
Guess I will have to get my tyre cutter out and do a bit of tyre retreading