The warning comes after the London Fire Brigade (LFB) experienced its “busiest week” in history last week.
London’s Fire Commissioner Andy Roe said “urgent action” was needed to introduce a national ban on the sale of disposable barbecues which he warned could cause “untold damage”.
Firefighters attended more than 1,000 fires in the week from July 18 as temperatures soared, taking more than twice as many calls as usual and tackling an unprecedented number of large grassland fires.
During that period the brigade received 8,302 calls, while on average it usually takes around 450 calls a day.
Mr Roe said people behaved “carelessly” and “recklessly” despite warnings about grass fires.
On Saturday July 23, firefighters prevented a serious blaze at Wanstead Flats, east London, caused by a disposable barbecue.
Mr Roe said disposable barbecues “can be bought for as little as £5 and can cause untold damage, especially when the grass is as dry as it has been over the last few weeks”.
He added: “Last week is another example of how we are increasingly being challenged by new extremes of weather as our climate changes and we’re developing long-term strategies to deal with more incidents like this in the future.”
Waitrose, Aldi, and other retailers have announced they will no longer stock disposable barbecues because of their detrimental impact on the environment and wildlife.
The UK experienced a heatwave last week with a record-breaking high of 40.3C in Coningsby, Lincolnshire, last Tuesday.
That day the fire service saw its busiest day since the Second World War as a result of the extreme temperatures, taking 2,670 calls and attending 1,146 incidents.
A total of 16 homes were lost in the large fire in Wennington, east London, and crews had to fight to save the fire station itself from the flames.
The National Fire Chiefs Council has warned UK cities they need to prepare for wildfires after dozens of “unprecedented” blazes broke out during last week’s record breaking temperatures.
Firefighters also shared tips on how to prevent grass fires which included not having barbecues on balconies, parks and public spaces.