Thank you all for your support and input.
I have some Crovect unopened on standby and I would strongly recommend this, when it happens you need the resources available quickly. ( Even though this time it didn't help me )
Picking the maggots off, in my case I'd have struggled because of the amount there were, a friend suggested the hosepipe to wash them off, works to a point. Many of us don't like to use chemicals and I'm at the front of the queue on that, but there are reasons for them being there and I would be more inclined to get in quick next time.
For info - I'd seen flies around the back ( backbone not bum ) of this sheep and didn't put 2 and 2 together. I did check her but of course at that stage it would only be eggs and too small to see.
So next time I see flies round a sheep I'm going straight in with the treatment and taking on board all the useful advice
on here, off to buy some Battles now. Have it on the shelf ready !! Thanks all.