Peat does not ignite spontaneously, especially not in its default state of wetness, so it only burns when it is dry. Britain has been suffering/enjoying [depending on your view] a sustained heatwave in which temperatures have soared. This may be connected with general trends in a warming climate, where the north of Britain suffers hot summers, but stormier winters; and this has been a hot summer! The result is that the peat is tinder-dry. A discarded cigarette, a spark from a camp fire or from an inefficient engine would be sufficient to set the fire off. I discount lightning as in Britain it usually occurs with heavy rainfall, which quenches the flames.
Moorland fires can be flash fires, which burn off the tops of dry heather and other moorland plants, often burning so quickly that insects survive; but when the peat burns you get a problem, for the fire can simmer under the surface,moving inexorably along without people noticing, to spring up elsewhere later on when you think it is quenched. This is what has been happening on Saddleworth Moor, where firefighters are finding that flames spring up in unexpected places, even where they have previously been previously extinguished. The best hope for firefighters dealing with a blaze like this is a heavy rain storm, but rain is not due until weekend, in three days' time. In the meantime we must keep the fire away from the residential areas in the towns, but there are sheep farms that need defending and that is going to be difficult. So far no one has been killed or injured, and the damage has been to animal life and property.
Moorland fires are not a new phenomenon, for they have a long history, even the Bronte sisters who dwelt on the moors at Hawsworth, encountered one. Fire is a natural part of the cycle of life on the moor, and it serves to burn off dead heather and provide scope for new shoots, but it is moderated by England's normally rainy climate. But as summers become hotter and drier there is a danger that moorland fires will become harder to control and more damaging. Gamekeepers have in the past and even in the present practised controlled burning of patches so as to provide variety of heather,as the new growth provides food for grouse. The grouse are bred for shooting and are maintained by gamekeepers. There is no evidence that controlled burning started these fires, and indeed no sane, self-respecting and competent gamekeeper or farmer would set off fires in the weather conditions that Britain is now experiencing.
While fire is an ancient phenomenon, on valuable land it damages important projects. We cannot prevent it, all we can do is minimize its occurrence and put it out as soon as possible.