Thanks Nigel,
I just learned something. I did not think about tyres having a weight rating. My tyres are AVON too, I think mine are 92V but I will check. I did not think about the risk of deflation, although I have seen that in cold weather.
You reminded me of an issue that came up on my SVA regarding design weights. I got the design weight numbers from Pilgrim which I put in the paper work. Then I failed my SVA because my car exceeded the declared design weight! As the car is build pretty standard clearly the Pilgrim design weight was wrong! Anyhow I got Pilgrim to send me an official letter declaring "corrected" design weights to show I did not just pull the numbers out my a*se, which what I suspect they did

Anyhow my "official" design weights are 490Kg front Axle and 580Kg Rear Axle. It amazes me that the rear axle weight is heavier than the front but I assume that is with allowance for passengers and luggage. I also have weights from the car at the SVA, I assume that was without me in it but I don't recall the specifics.
Anyhow armed with this I will look on the internet for how to calculate the tyre weight rating and perhaps tyre pressures
PS I did not understand your comment about leaving the tyre on the road.