Thanks, I'll get one on order.

Today's Update: Without doing anything to my car since yesterday, I tried to start it - started fine, so after about 30-60 seconds, I stopped the engine and tried again - started fine. So then as I replaced items (ECU plug securing strap, ECU into 'fitted' position, battery cover, pretty much any item I had removed), I tried a re-start - and every time it started! I then went for a tentative drive -all seemed good (with one slight exception being my Cruise Control but that is not related to this fault) but I waited until I got home before stopping the engine once more, then tried restarting it again - yup, it started fine.

So, nothing has been replaced, a few plugs / socket / wires have been jiggled and now it seems ok - but of course, confidence is slightly lacking at the moment....

I'll start a new thread about my Cruise Control - it's a sticky switch, so nothing to do with any of this.