Climate editor by Justin Rowlatt.
Some shooting estates in England burn moorland despite a government ban.
The deep soils of England hold huge amounts of carbon.
Peatland vegetation has traditionally been burned to create and maintain habitats.
In some protected areas of England, there is a ban on burning deeper than 40 cm.
Peatlands cover 12% of the land in the UK and store an estimated 3 billion tonnes of carbon, equivalent to all the forests in the UK, Germany and France.
The amount of carbon they store has been called England's national rainforests by the government.
Evidence collected by the bird protection charity, the RSPB, and the environmental campaigning organisation, the Greenpeace organisation, suggests thatrainforests are still being set on fire illegally in England.
According to the government, any cases where a violation of consent or regulation is suspected will be investigated.
Burning clears the way for the new green shoots grouse like to eat, but also releases stored carbon into the atmosphere.
The season for burning on upland soils is from 1 October to the 15 April each year.
When the government introduced the new regulations, they said there was consensus that burning vegetation on blanket bog was damaging to the environment.
There are large areas of deep peat soil in Blanket bog.
It said the new rules in England were intended to help the UK hit its target to cut emissions to net zero carbon by the year 2050.
If a licence has been granted or the land is steep or rocky, but no licences were issued during the latest burning season, the government will allow the ban to be lifted.
The Moorland Association says careful burning has been a part of moorland management for more than a century.
It says that well managed burns can promote biodiversity and reduce the risk of wildfires, and that vegetation typically recovers from well managed burns within three years.
The government has received evidence from the RSPB that it believes is in violation of the new regulations. It has created a mobile phone app that allows people to report burns.
A high tech approach has been taken by the group. It used a NASA satellite to identify hot spots in areas shown on government maps as protected peat moorlands.
Satellite images were used to confirm fires had taken place.
There were sometimes fires visible in the images.
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The researchers compared before and after pictures to identify burn scars where cloud cover made it impossible.
The estates were visited by the BBC.
We found burn scars at and around the coordinates identified by the satellite data at the Bowes estate in the Yorkshire Dales National Park.
Dr Ben Clutterbuck, a leading expert on UK peatlands, helped us test the peat and found it was deeper than 40 cm.
The letters were delivered to the registered address but there was no reply.
There was no evidence of burning at another estate. The area where the fire was set was less than 40 cm deep.
On both estates, we stayed close to a public footpath and did not disturb any ground-nesting birds by walking on burnt heather.
The group visited two estates. There was no evidence of burning on deep peat. The reason some sites were found to be illegal burns is because the government map it used as a guide was not definitive.
"Our findings show how important it is that all the locations we have identified are confirmed with site visits," said Emma Howard, a researcher with the Unearthed unit.
The Moorland Association welcomed the government's investigation.
It said its members would help with any queries. They would continue to follow best practice guidelines.
There is a call for a blanket ban on burning on all peat.
Dr Patrick Thompson, a senior policy officer at the RSPB UK, said that intensive and damaging land management practices such as burning continue to harm and threaten nature.
Why is the government allowing owners of moors to turn swathes of national parks and protected sites into charred wasteland for private gain?
The Labour Party wants to extend the ban to cover all the moorland.
According to the International Union for the Preservation of Nature, 80% of the UK's peatlands are in a damaged and deteriorated state because of land management activities.
It estimates that the UK's damaged peatlands are releasing more CO2 each year than all the households in Edinburgh, Cardiff and Leeds combined.
As the climate changes, the emissions are likely to increase.