Just a thought.....pylands tend to be fatties....are they too fat and is that causing the problems? Just a thought!
This is a very good point - ewes at lambing should be fit, not fat and remember that overfeeding can result in larger lambs, so harder births.
How long I would leave a ewe where the lamb is normally presented would depend to some extent on how old she is. A first time lamber will need much longer than an older ewe - she needs the time for everything to stretch and open up and if you intervene too soon, you risk damaging the ewe.
Generally outcomes are much better if the ewe is given the time to deliver the lamb herself. In an older ewe, an hour is not too long and I would be quite happy to leave a first time lamber twice this long (given that she is not exhausted or distressed.
I know when I was having my first child I was in second stage labour for 2.5 hours, and I was left to get on with it. So I am happy to leave the ewes to it, but you do have to exercise judgement.