A Home Office source confirmed reports that fire safety issues did lead to initial setbacks, saying a door had been put on the wrong way round.

But now that has been fixed, there is another hold up because the Health and Safety Executive (HSE) is looking at working practices for port authority workers, they added.

The Fire Brigades Union (FBU) said it believed the vessel was a "death trap", but Net Zero Secretary Grant Shapps dismissed the claim, telling ITV there was "no reason why it wouldn't be absolutely safe".

A government source also accused the union of a "betrayal of our country and the British people", telling Sky News that their real reason for opposing the barge was "because it suits their political games".

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The barge, which is currently docked in Portland on the coast of Dorset, was supposed to start accepting arrivals last week, but the date was pushed back as more work was needed.

The first people were then due to move on to the vessel on Tuesday this week, but that plan was also held up after last minute meetings were held responding to fire safety concerns.

Prime Rishi Sunak denied getting the barge up and running had been a "shambles", telling LBC: "The point here is not is it next week, is it yesterday, the fact is this is an example of me doing something different that hasn't been done before to help solve a serious problem.

"It is in the process of being done, there is a barge here, people are going to be put on it, which will ease pressure in local communities and save [money]."

Asked if the vessel will be ready for next week, the PM replied: "The Bibby Stockholm will be in operation as soon as it has passed all the checks and regulations, as soon as possible, that is the key thing."

The 222-bedroom Bibby Stockholm will eventually house up to 500 male asylum seekers who are currently staying in hotels, as the government seeks to cut its accommodation costs while their claims are processed.

But the current plan is to start with 50 people - when the vessel is ready.

The barge will have 24-hour security and accommodate single men only, who will sleep in bunk beds with between two and six people per en-suite room.

Reports of fire safety issues surfaced in recent days, with the FBU claiming the government was taking "a reckless approach to the safety and well-being of both vulnerable refugees and firefighters".

The FBU is planning to write to the Home Office about overcrowding and access to fire exits on the vessel.

'Accident waiting to happen'

Ben Selby, the assistant general secretary of the FBU, told Sky News the union's primary concern was the barge was designed to fit 222, people but the Home Office wants to use it for more than double that capacity.

He said: "Our main concerns are focused around those large numbers trying to pass through narrow doorways, trying to pass through narrow corridors, and I leave this as an open question - if firefighters were needed to make entry on to that, through those narrow corridors, when people were seeking to escape from it in case of a fire, how would they ever reach the seat of that fire and be able to make the necessary rescues?"

On the scale of risk, Mr Selby referred to the concerns raised prior to the fire at Grenfell Tower which "were largely ignored and saw the loss of 72 innocent lives".

He said: "We don't want to be in the case right now. We feel like we're looking down the barrel of another possible disaster.

"We believe it to be a death trap, and we believe it's another accident waiting to happen."

Asked about the concerns on Tuesday, Mr Sunak said: "All migrant accommodation has to go through a series of checks and inspections to make sure it complies with regulations. That's what's happening in this case.

"This is ultimately about fairness. I don't think it's fair that British taxpayers are forking out £6m a day to house illegal migrants in hotels."

The vessel has attracted a backlash from local Tory MPs as well, with Chris Loder demanding to see safety reports, claiming the barge was going to house double the amount of people it was designed to hold.

A Home Office spokesperson said: "The Bibby Stockholm is undergoing final preparations to ensure it complies with all appropriate regulations before the arrival of the first asylum seekers.

"This is part of the government's plan to reduce the use of expensive hotels and offer alternative accommodation that is more manageable and better value for communities, just like our European neighbours are already doing.

"We continue to work closely with Dorset and Portland councils, as well as the local NHS and police services, to manage any impact in Portland, including providing substantial funding to local services, to address the local community's concerns."