Portsmouth tower blocks: Leamington and Horatia House will be torn down – and were at risk of ‘collapse’ after gas canisters found last summer

It comes as it was revealed that dangerous gas canisters were found at Leamington House and Horatia House, in Somers Town, after it was announced there were fears the buildings could crumble in an explosion.

Councillors at the city council's cabinet today ordered the demolition of the blocks amid fears for residents' safety - and after being told dangerous canisters were found after a planned evacuation.

Officers' recommendations to take down the high-rises were agreed with potential for new social housing to be built on the sites, rather than refurbishing the blocks at a cost of around £86m.

The move came after weaknesses were found in the buildings' concrete last year when their Grenfell Tower-style cladding was removed. It was thought the structures could not withstand an impact such as a gas explosion.

Although there has not been piped gas into the homes for almost 30 years, during the start of the evacuation process last year five potentially dangerous gas canisters were found on site, the Portsmouth City Council cabinet meeting was told today.

Housing maintenance officer Meredydd Hughes said: 'During the face to face meetings that we had with residents after the announcement last year we found five canisters offered up by residents when we visited their homes and stores.

'These were three small camping cylinders and two larger patio gas canisters which were 2.5kg in size.'

Councillor Matthew Winnington, cabinet member for health and wellbeing, told the meeting: 'We have to put the safety of the residents first.

'It is very interesting about the canisters that were in the blocks and I think that unless you're going to have some kind of Big Brother-style authoritarian state in the city people will always take things into their homes that maybe they're not supposed to.'

The council's head of building maintenance, Steve Groves, explained what a gas explosion could mean for the towers. He said: 'If there's a disproportionate collapse that is where a small area of damages has occurred in the structure and that will lead to the collapse of a major part of the structure.

'That would mean in essence you may have a small explosion in one room but that may have an impact progressively on the rest of the structure and a number of floors may collapse as a result.'

Councillors agreed that the redevelopment of the site would provide a chance to at least match the 272 social homes that will be lost, as well as building private homes to ensure it is sustainable.

Housing boss, Cllr Darren Sanders, concluded: 'This has been incredibly challenging for everyone, especially the families living there. The truth is really simple that we have to put safety first. The risk of a partial collapse and the gas canisters really does concern me.

'This is the second time in 20 years that we have had to move people out of the buildings. They deserve a long-term solution, not just a sticking plaster.'

Once all households are moved out by the end of spring the towers will be decommissioned before work to deconstruct them can begin.