London Bridge and West Bermondsey councillors Emily Hickson and Sam Dalton asked the borough's overview & scrutiny committee to probe the major works project at Devon Mansions at a meeting on Wednesday night.
Devon Mansions is a collection of five Victorian mansion blocks along Tooley Street - adjacent to the council's headquarters.
The blocks are council-owned and are run by the Fair Community Housing Services tenant management organisation. Many of the flats were sold under the 'right to buy' legislation and are now owned by leaseholders.
In 2020 the council initiated a £5.9 million project to complete internal and external works, including asbestos removal and fire safety measures.
The works were due to take 13 months but ended up taking just over three years.
The contract was awarded to French-owned Equans (formerly Engie), with CalfordSeadon hired to manage the project on behalf of the council.
Cllr Emily Hickson described the situation at Devon Mansions as "the most distressing housing issue in our ward in terms of failures by the council".
"We believe there have been serious failings deserving proper scrutiny, both with the works themselves and with the communications to residents while the works have been going on," she told the cross-party committee.
"Since we were elected in May 2022, it's been clear that there been a number of very serious weaknesses with the major works, which are very serious and damaging to residents.
"Number 1: the cost of the works. Number 2:, the poor quality of the works and the risk involved. Number 3: communications with residents. And number 4: staff performance."
"So we've gone from an initial contract for the works having a total of £5.9 million to a position where they've cost over £10 million.
"This is a huge increase in costs and suggests something has gone seriously wrong in the management of the project by the council."
Cllr Sam Dalton added: "There seem to be serious weaknesses with staff performance in the major works team during this project.
"It's been clear at various points throughout the works that members of the council staff have not been performing to a high enough standard.
"We are aware of some suspensions and disciplinary proceedings against some individuals connected to this.
"We therefore think that this experience should lead to a full review of the major works team and its performance with recommendations on how this team can function to a higher standard going forward."
Devon Mansions resident Ina Negoita told the committee that the poor quality of the work amounted to "sheer vandalism".
She set out how tenants and leaseholders had been "treated like retards" when they challenged aspects of the works.
"We plead with you to start an investigation," she said.
Cllr Darren Merrill, cabinet member for council homes, said: "What I really want to do is thank the residents for the work they have done to bring this investigation to light and also to say sorry to those residents that it has come to this point and that we are having to sit here and go through that."
He added: "Clearly, things have gone wrong. I have given a clear political steer to the officers to get to the truth, let me know what recommendations are coming through and we will put those into action."
David Quirke-Thornton, interim strategic director for housing, said: "There is no other way to respond to the concerns that have been raised than to apologise unreservedly to the residents.
"The failings here have led residents down, they've let councillors down and they've left the council down.
"I have said before and I'll repeat it again tonight: I will never defend the indefensible. Southwark is better than this."
Promising to follow due process, he said: "Officers involved in these failings will be held to account."
He warned that there was a possibility of launching a fraud investigation if an audit suggested that was necessary.
"We are committed as a council to remedying and resolving these failings and ensuring that this does not add costs for leaseholders or residents."
Mr Quirke-Thornton said that remedial work at Devon Mansions will begin in January, but investigations into the failures could take till summer 2024.
Cllr Victor Chamberlain, a Lib Dem member of the overview & scrutiny committee, said: "This is absolutely gross mismanagement. Maladministration, negligence... you name it, it's here.
"At the moment I just don't have any confidence that this council has got any ability to manage major projects like this – and residents in the borough shouldn't either."
Mr Quirke-Thornton - who has been looking after the housing department since the departure of the last strategic director - revealed that he has instituted a "complete lockdown" of procurement decisions since he took over.
"I have suspended the scheme of management in the housing department, which means that no contracts can be authorised by anyone except me," he said.
"That's a very radical position to take but as the chief officer currently responsible for that department, unless and until I'm assured that all of the procurement arrangements are correct, no-one in the department may authorise a contract except me."
It's nine years since the council apologised unreservedly for a catalogue of failings during similar major works at Draper House at the Elephant & Castle.
That 2014 apology was made by Cllr Ian Wingfield as cabinet member for housing. Nearly a decade later, Cllr Wingfield now chairs the cross-party scrutiny committee.
Wrapping up the discussion on Devon Mansions at Wednesday's meeting, Cllr Wingfield said: "We've heard about the investigations which are going to take place.
"We've heard from the officers their sincere apologies, and the fact that this should never have happened in the first place.
"It's shocking for all of us that we're here this evening having to talk about this matter in such great detail, and the distress that it's caused individual residents, which we're all sorry for and should never have happened.
"The key thing is for us to ensure that those investigations are carried out in a proper and full manner, that all issues are dealt with and that anything that has to be referred to an outside agency is done so."