Firefighters have voted by almost 4-1 in favour of strikes in a row over pensions, threatening the first nationwide walkouts in a decade.
Members of the Fire Brigades Union backed industrial action by 18,277 votes to 5,166, a majority of 78%.
The union said planned changes to pensions were "unaffordable and unworkable", would impose an increase in members' contributions and would put firefighters at greater risk of dismissal without access to a proper pension if they cannot maintain fitness standards as they approach the retirement age of 60.
FBU general secretary Matt Wrack said: "Expecting large numbers of 60-year-olds to fight fires and rescue families is dangerous to the public and to firefighters.
"The Government is simply ignoring the evidence about the physical demands of firefighting and has been unable to answer our concerns during two years of negotiations.
"None of us want a strike, but we cannot compromise on public and firefighter safety. We hope common sense prevails, and the Government returns to the negotiating table."
The FBU said it held the ballot after almost two years of negotiations, adding that it faced a July 12 deadline for the proposals to be accepted, or face imposition.
Mr Wrack said: "We cannot expect large numbers of firefighters in their late fifties to fight fires and rescue families without creating danger to the public and firefighters.
"We have repeatedly raised safety concerns and provided strong evidence to back it up but the Government just isn't listening.
"This result is a clear indication of the anger felt by firefighters. It's still not too late for common sense to prevail if the Government are willing to return to the negotiating table."
The union said the Government's own figures have shown that thousands of firefighters could face the sack without access to a proper pension simply because they are getting older.
Fiona Twycross, Labour's fire spokesman on the London Assembly, said: "[The] ballot for industrial action may look strange to the public, but the fact is the Government are trying to force firefighters to work until they are 60.
"Currently they can retire on ill-health grounds before 60 and retain their pension. Under the Government's plans, if a firefighter is deemed unfit before they turn 60, they will lose part of their pension. The Government is being cynical as it knows from their own review that this will affect two-thirds of firefighters."
Labour said the dispute was happening against the backdrop of plans to close ten fire stations in London with the loss of 552 firefighters' jobs under cost-cutting measures.
London Fire Brigade said it was prepared to deal with a strike, having already removed 27 fire engines from stations, which will be used to cover for any walkout.
If the strike goes ahead, the 27 engines will be deployed at strategic locations across London to provide fire cover for the capital. The contingency fire service will be provided by a contractor, supplying basic firefighting and some rescue work, said the brigade.
Fire minister Brandon Lewis said: "This Government does not believe that industrial action is necessary. The pension on offer to firefighters is one of the most generous in the public sector. The FBU is creating a smokescreen around the issues of fitness and retirement age to justify their behaviour whilst ignoring the facts."