A disposable barbecue is the most likely cause of a big blaze at Studland in Dorset, the local fire service has said.
Ninety firefighters and ten fire engines – including some called in from neighbouring areas – were sent to the scene after the flames were reported at 1pm on Friday.
There was “evidence of a little 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% that was the cause but when we find evidence we have to assume that’s the most likely cause,” a spokeswoman added.
“Fires don’t just start on their own.”
Firefighters worked through the night to bring the flames under control.
Dorset Police said on Saturday afternoon that an unexploded piece of ammunition believed to date from the the Second World War had been found on the scorched heathland.
A bomb disposal unit would be attending, the force added, with the public warned to expect a loud bang.
In the first 10 days of August, DWFRS said it had attended 180 wildfires.
In the same period last year it was 34.
Staff have “never had a year like this one – it is just unprecedented”, the spokeswoman said.
Temperatures could reach 35C this weekend.
An amber heat warning has been issued by the Met Office.