Your Orpingtons may be more inclined to brood since you're in England. Here in the US, most of our hatchery stock has had the broodiness bred out, or down quite a bit.
I'm going to toss out a vote for Dark Cornish. Mine were fantastic broody mommas, even sneaking away and hatching clutches in the blackberries I knew nothing about . Large, meaty birds, good foragers, decent layers. No feathers on the legs