In a development with potentially major implications for blocks elsewhere, residents of the Ledbury estate said they were shocked and alarmed to learn that the four 13-storey blocks were at risk of collapse in the event of a gas explosion in one of the flats.

Southwark council, which owns the blocks in Peckham, south-east London, has sent a letter to residents of the 242 flats saying they will have to “temporarily decant the blocks over the coming weeks and months” for emergency works.

The council has immediately ordered the gas supplies to be cut off, leaving most residents without cooking facilities, hot water and heating. The letter said officials would distribute electric hotplates and that residents could take showers at a local leisure centre.

The discovery that the blocks are structurally unsafe heralds a potential new series of safety worries about high-rise flats, which since the Grenfell Tower blaze have mainly been focused on fire safety, notably flammable cladding.

Arnold Tarling, a surveyor and fire safety expert who first spotted the problem at the Ledbury estate, said it was likely there would be many other blocks around the country with similar problems.

The Ledbury blocks were constructed between 1968 and 1970 using a method called large panel system, in which giant concrete sections were bolted together on site. The same technique was used at Ronan Point, a tower block in east London which partly collapsed in 1968 following a gas explosion. Four people died and 17 were injured when a blast from a gas stove in an 18th-storey flat caused a series of floors to collapse on to each other, one of the most notorious public disasters of the era.

An investigation said buildings built using the same method must be reinforced, or else have no gas supply. Southwark council, which took over the Ledbury blocks from the former Greater London Council, said it believed they had been strengthened.

After the Grenfell Tower blaze, which killed at least 80 people, worried residents urged action over big cracks in walls between flats on the estate, which they feared could allow a fire to spread through a block. They asked Tarling to check the cracks, but while on the estate he raised parallel concerns about the gas supply, identifying the structure as potentially unsafe.

Southwark had already employed engineers Arup to examine the blocks, and on Thursday the council wrote to residents saying its belief that the buildings had been reinforced “may not be correct”. The gas supply was being turned off and locals would be moved out, the letter said.

A council spokeswoman said it was not yet known how long residents would need to leave for, as this depended on further surveys.

One resident, who asked to not be named, said she was appalled to learn she had been “living for years in a death trap”. “I cannot describe my level of anger at Southwark council,” she said. “Not only is the gas supply illegal, but the structure of the building is potentially unsafe. It’s a miracle no one was killed over this time.”

The resident said it was an insult to ask people to shower at leisure centres, saying they should be moved to hotels. “We’ve got people in their 80s, who are blind, who are being asked to traipse along with their towels and a change of clothes.”

Tarling said he was aghast at the safety lapse. “As soon as I walked in and saw the gas supply, I knew it was all wrong,” he said. “Southwark council did not listen to me, and you really have to question their competence.”

In a statement, Southwark’s deputy leader and cabinet member for housing, Stephanie Cryan, said: “We didn’t own the blocks when they were constructed at the end of the 1960s, but all the reports we found suggested the blocks were strengthened following the Ronan Point incident in 1968 to make them safe to include a gas supply.

“Arup’s structural investigations suggest this strengthening may not have occurred, and we have therefore turned off the gas until further investigations can be done.”

The council had written to the Department of Communities and Local Government about the issue, she added, “as it may well have implications for other blocks around the country that were constructed in this way”.