Took it down to the bloke who actually owns the engine (not that he wants it back!) and he had a bit of a look. Yes, you can actually see the water in the cylinders, through the spark plug holes. I'm going to say maybe its a cracked cylinder head, more than just a blown gasket. Over only a short period of sitting one of the cylinders had a good inch or so of water in it. Still drives alright, in fact better since he only put the rad cap on half way to lessen the pressure.

What is it about the design of A series motors that they can be all but completely rooted and blow smoke like a steam train but still pull strongly ? I've seen in magazines where there's a VW show each year and they stick a VW motor built from spares in a cage and run it at redline till it blows , normally fairly soon after starting . I've been tempted to do that with a near dead mini motor but I'm sure it'd just keep revving till fuel or oil ran out . I've killed many mini motors but nearly all through wear , only two were bearing failures and they were caused by a dodgy clutch master cylinder . They's tough little beasties .....