
Thanks Moose!
The bike needed a damn good scrub & wash but it's in better condition than I was expecting and... IT FITS!

I'll have to measure the frame sometime, it seems to be almost exactly the right size for me, I don't have to stretch too far to reach the bars and I can easily get both feet flat on the ground standing over the top-tube.
Once I've put a proper saddle and pedals on it I'll post a photo for posterity.