Other grass fires have broken out in scorching conditions – with firefighters warning that people continue to barbecue in parks and throw cigarettes out of car windows.
Ten fire engines and around 70 firefighters were called to a blaze in Enfield, north London, on Saturday afternoon.
An area measuring around 900m by 600m was on fire, the London Fire Brigade (LFB) said.
The fire produced a lot of smoke on the M25 between junctions 25 and 26, he added.
“The tiniest of sparks can ignite a fire that could cause havoc,” he said.
“Despite our continued warnings over the past few weeks, we know there are still people barbecuing in parks, throwing cigarettes out of car windows and leaving trash lying around.”
The Cornwall Fire and Rescue Service said it was battling a major wildfire in the town of Camborne.
Nottinghamshire Police are appealing for information following a large fire in a field in Mansfield.
“A nearby house and a number of vehicles were damaged due to the fire, which is currently under control by firefighters,” the force said.
Kent Fire and Rescue Service said they sent 10 fire engines to a crop fire in the village of Wye.
In Dorset, the local fire service said a disposable barbecue was the most likely cause of a large fire on Friday.
Ninety firefighters and ten fire trucks – some called in from nearby areas – were dispatched to the scene in Studland.
There was “evidence of a small camp where someone had used a disposable barbecue”, the Dorset and Wiltshire Fire and Rescue Service (DWFRS) said.
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“We can’t say 100 per cent that was the cause, but when we find evidence we have to assume it’s the most likely cause,” a spokeswoman added.
“Fires don’t start on their own.”
Firefighters worked through the night to bring the flames under control.
Dorset Police said on Saturday afternoon that unexploded ordnance dating from the Second World War had been found in the scorched moor.
A bomb disposal unit would be present, the force added, with the public warned to expect a loud bang.
In the first 10 days of August, the DWFRS said it witnessed 180 wildfires.
At the same time last year, it was 34.
Staff have “never had a year like this – it’s just unprecedented,” the spokeswoman said.
Temperatures could reach 35°C this weekend.
An orange heat warning has been issued by the Met Office.