Thank you all for the information and tips, much appreciated, we unfortunately lost two lambs in total, but I have successfully managed to rear twelve lambs and they are extremely healthy, I was rearing these to go to market but unfortunately have become too attached to them, so I am going to breed from them and their offspring will be going to market (providing I dont have to hand rear them).
To refresh, we've just had a ewe lamb scouring quite prolifically (like one of those mustard dispensers you get on burger stalls!) and our local sheep guru reckons that it wa just greed - a single lamb getting too much milk from a yearling ewe with udders the size of Belgium.
Thankfully the problem seems to have cleared up now.
Little sods, though - they'll always find a new way to worry you!
On general sheep welfare, I found a very useful pdf guide published by the Department of Agriculture for Northern Ireland here.