OK, so diagnosis completed.....
Cambelt has slipped 1, maybe 2 teeth which caused a backfire which blew the inlet manifold. Very, very unlikely to have damaged any valves (thereis a teeny possibility) so more fingers crossed.
The garage I had it recovered to (FAST in Stockton - an Alfa specialist) got the price for a new manifold & gaskets which is... wait for it... £910
Plus the belt & tensioners which after labout came to over £1600
However, the friendly chaps at BMC in Aycliffe have a 2nd hand manifold so that brings the price down considerably to around the £750 mark, still not cheap but a bit easier to stomach.
So, going to have to bang that on the credit card and it looks like the 147 will be going after it's fixed & all better (anyone want it for £5k??
), and I probably won;t replace it with another Alfa (yet).
Hope I'll still be welcome round here if/when that happens, I'm still undecided.