Got under the bonnet this morning. Couldnt find the idle switch -seems to be right under the throttle body. However, opening the throttle and then closing it, there was a click when it closed. I guess this means that switch is ok......
Changed the ISV with the scrappy one and it seems to be behaving itself more than it was. The revs still drop off but nowhere near as bad as it was yesterday. Looks like the other ISV was the culprit this time......

Bloody car does my head in, always going wrong - Fords look reliable in comparison lol

Thanks for all the advice.........