Well we pulled them all in. On further inspection it just seems like the one isolated case although all have been retreated as they were due to have crovect this week.
The lamb that has the strike... well we caught him, and started to clip the bit that we could see was struck, then kept clipping... and clipping, and clipping. He's pretty much got a saddle shaped clip on his shoulders/ back now, very strange his back end was clean too. They had just started to penetrate the skin so we've isolated him, treated with crovect to which it brought out all of the maggots buried inside him, and I'll go back down after dinner to give a shot of Alamycin and some creep as he's looking a little sorry for himself now.
I'm kicking myself because I had the crovect ready to treat this week but we just never got round to it as OH is busy on harvest but it's sorted now. We ran out of crovect so need to pick up some more tomorrow to treat the last 3 lambs but at least he is sorted now. I've got some summer fly cream to put on him too especially for flystruck sheep which should help once all the maggots have come off.