B31 (1951) front brake woes.

[Beeza jon]

Well, after further thought, and  bit more head scratching I decided to look at the simple things first. I removed the mudguard and centre stay (brace) and had a good look at everything. There was a small amount of perceptable tension as I released the brace, and that struck me as of note.
It was out of true "in plane" and the mudguard itself appeared to suggest that it could be a pattern part, as it fitted quite awkwardly.
I refitted the brace, and adjusted it with gentle encouragement so that it no longer fouled the tyre. The wheel fits just as it should (and did previously) but now has the correct size tyre (325 still fitted).
However, the "as recieved " mudguard really doesn't want to go back on (in any useful position) and strongly suggests that its original fitment may well have been somewhat of a struggle to a previous owner (the bike was restored in the 90s).
So, I think that I will be quite happy to fit a plain alloy mudguard and live utilise the stays from the previous.
Aside of all that, I've been for a test ride, and the new tyres are great.
Once again, my thanks to you all for your help.