Ok, so decided to phone the ecu folk who originally tested it. I thought being as they had already been paid for the initial test, I'd give them a chance to redeem themselves.
Actually, it was quite a positive conversation and I put it to them that maybe the test they did didn't give the ecu long enough to warm up and the fault to appear, so I suggested that the only way to be sure was to actually try another ecu, rather than sending me back the original. They agreed and as luck would have it, (not my usual luck), they had just one in stock. He said to post mine back to them and they would use it to recode the other.
Sent it back first thing this morning, so may be back by Wednesday, which would be nice as I'm now on my annual holiday leave, and a car (that worked), would be nice.
It is going to cost me another £165.00 + vat and postage, but to be honest, as long as it cures by problem, I don't care. On the other hand, if it doesn't, I think I'll just have to shoot myself. :lol: