Fire chiefs consider setting fire to Saddleworth Moor to stop out-of-control blaze

Defensive burning works by lighting a controlled fire to remove the fuel in front of an advancing blaze. The Army may also dig wide trenches around the perimeter to stop it spreading further, a tactic often used when fighting Scottish wildfires.

Tony Hunter, assistant chief fire officer of Greater Manchester Fire and Rescue Service (GMFRS), said they had seen ‘significant improvements’ as helicopters dropped water and firefighters used paddles to beat out the flames.

But he added: “I would put an air of caution there though, we had a similar occasion where we thought we were on top of it and it flared up.” He also warned that if the wind changed direction the remaining moor would quickly set alight and said the blaze could last for weeks.

Mr Hunter said a good downpour of rain was needed to saturate the dry ground and vegetation - but none is forecast for days as the heatwave continues.

However experts warned that the underground peat may keep smouldering even if rain put out the flames and that industrial pollution locked in the peat could cause health problems for huge numbers of people.

Vincent Gauci, Professor of Global Change Ecology at The Open University, said: “The close proximity of these peatlands to centres of human populations such as the Greater Manchester area means there’s potential here for poor air quality to affect many tens of thousands of people.

“Saddleworth Moor has been a sponge for regional pollutants for centuries as the region was an engine of the UK’s industrial revolution.

“With none of the current pollution abatement strategies in the early industrial period, these moors were on the receiving end of a whole range of quite nasty industrial pollutants which could be remobilised in the current fires with unknown consequences for human health.”

Dr Bjorn Robroek, peatland researcher at the University of Southampton, added: “These fires can continue even when it starts to rain.”

On Thursday nearby residents who had been evacuated from their homes were allowed back but warned to wear face masks, stay indoors and keep their windows closed.

But doctors said people had reported bleeding noses, eye irritation and chest problems.

Dr Richard Bircher, of Lockside Medical Centre in Stalybridge, said about half the emergency appointments booked on Thursday were from patients reporting problems as a result of the smoke.

He said: "People are worried about it. They are minor symptoms but people are a bit scared."

He said the smoke was also exacerbating problems for people with asthma.

"Thankfully the smoke is getting less at the moment, but the advice is to try to avoid it," he said.

Dave Saxon, director of operations at Tameside Council, said the local authority was monitoring air quality.

Farmers have also been battling to save their animals from the seven foot flames. James Crother, 30, of Upperwood Farm in Oldham, fought through the blaze with family, friends and sheepdogs to move more than 3,000 sheep to safer fields.

One badly burned sheep was spotted wandering across the charred moorland after becoming separated from the flock, and Mr Crother believes many animals have died in the blaze.

“The smoke was so thick and the flames between six and seven foot high across the field,” he said.

"We just waited for gaps in the flames to rush through to be able to move the sheep.""I have seen grouse die, I have seen pheasants die, I have seen deer die.

Fire chiefs say they are "not confident" of finding out how the fire began, given the size of the blaze, but there was no evidence it had been started by BBQs or off-road bikers.