Thanks for the input guys, really appreciated.
Worms were a first thought as I approached this morning, but on closer look I could see it wasn't. I've also double checked under the tail, and it is from the vulva.
The ewe appears fine. I've not seen any sign of stress or infection in any of them, they've all been acting as usual, the first sign of something untoward was the ram sniffing and pushing her (I can see them from the house, and look at them out of habit too many times a day to count). Currently still on grass (with mineral lick), and the odd bit of hard feed to get them over for a checkover, they are all eating ok (she was 2nd in the race to the bucket this morning).
No smell that I can detect (although the ram clearly can, as has been having a good sniff). Ram was home bred. Unrelated.
I don't know if what I can see is pre or post abortion? Looks post to me if last years lambing is a guide to go by, but it's my first year and I'm still a novice in so many respects. I've checked the field but 'a foetus that can fit in your hand' - easy to miss, so I may have. Thanks for that guide shep53, I was looking for something larger so I'll pop out there again.
I have no idea if she was/is carrying a multiple birth. If so then maybe the other will go full term? I'll note the possibility down in her records; but I'll change the raddle colour anyhow, and see if she comes back into season in due course.
Am still monitoring her as need to make sure this is attended to and make sure she is ok.