Peter, I think my Avons safety wheels have 215 tyres on them but the spare will fit in the wing bay - you just need to remove one or two black painted wood blocks which provided a limit/rest for the narrower steel wheel.
Now you just have to find a tyre fitter who can follow the instructions on how to remove and fit tyres on those wheels!
http://www.bristolcars.info/forums/showthread.php?t=41