The Wennington wildfire which tore through 17 houses was likely to have started in a garden, a London Fire Brigade investigation concluded.
A neighbour spotted the large grass fire in the village near Havering, east London during scorching temperatures at about 1pm on July 19 last year.
While investigators were unable to determine the exact cause of the blaze, a large caravan was noted as an early area of where it began.
Firefighters added they had not fully discounted that it was deliberate, a discarded cigarette or sunlight on a glass fragment.
An examination of the scene and video evidence found that the fire originated “in or around” the bottom of one of the gardens, although given the wind direction it could have started on the marshland to the rear.
A large static caravan was noted as the “perceived area of origin”, as it rapidly caught fire and helped the blaze spread.
In total the fire spread across 40 hectares, damaging 17 houses, five garages, 12 stables, a car repair workshop and several vehicles, as well as numerous sheds and outbuildings.
The investigator wrote: “Having called the brigade, [the neighbour] attempted to stop the fire spreading using a hosepipe, however, this had little effect.”
The conditions were “exceptionally hot and dry”, the investigator added, which meant the flames could easily move along the marshland to the rear of the properties.
LFB were able to stop a grass fire spreading to a diesel tank in the yard of Wennington Fire Station, which neighboured the yard containing hazardous cylinders.
Havering Council leader Ray Morgon said: “The fire caused massive disruption to residents in Wennington.
“We continue to be there to help the people and families affected to rebuild their lives and I hope the publication of this report will serve as some form of closure after what has been an immensely difficult year.
“Whilst the report does not provide a definite conclusion on the cause of the fire, one thing we can conclude from the findings and guidance is that fire safety is everyone’s responsibility.
“As we enter the summer months and the likelihood of higher temperatures it is up to us all to take measures to prevent this type of horrific incident from happening again.”
Neil Guyett, LFB’s interim borough commander for Havering, said: “Last summer, Havering experienced a number of significant fires and our thoughts remain with those impacted by the devastating fire in Wennington.
“Following the fires last summer, we have been working hard to prepare for what could be another summer of extreme weather temperatures.
“We know last summer was not a one-off - climate change will continue to give rise to more extreme weather events.
“Firefighters have been receiving enhanced wildfire training, and this week we introduced new Holey Hoses which we can use to help protect life and property when a significant grass fire or wildfire breaks out.
“We have already tackled numerous grass fires in the borough this summer, such as at Hornchurch Country Park, and we need the public to help us.
“It is so important that people dispose of litter and smoking materials properly when they visit parks and open spaces by ensuring rubbish is placed securely inside a bin or take it home with you.
“If you have had a cigarette, please make sure that it is completely out. Any spark can ignite a fire especially if the ground is dry.
“Never take a disposable BBQ either - they are officially banned in Havering’s parks and open spaces and we would urge visitors to respect this ban.”
