The plans have been criticised by local groups, refugee charities and Conservative MP Richard Drax, who said "every action's being looked at", including a legal case.

The vessel, which is currently in Italy, will be "significantly cheaper than hotels", says the Home Office.

The government has not given a costing.

The three-storey barge called Bibby Stockholm will be located at Portland Port off the coastal town of Weymouth, and used to house single men while they wait for their asylum claims to be processed. It will operate for at least 18 months.

As well as providing basic and functional accommodation, healthcare and catering, the berthed vessel will have security on board to minimise disruption to local communities, says the Home Office.

The boat, with 222 rooms, has been refurbished since it was criticised as an "oppressive environment" when the Dutch government used it for asylum seekers.

Bibby Marine, which owns the barge and will lease it to the government, said there was a laundry and a canteen on board - and all the rooms have a window, bed, desk, storage and en-suite.

It said the boat "has comfortably housed workers from various industries including construction, marine and the armed forces over the years".

Housing migrants in hotels costs more than £6m a day, says the Home Office, with more than 51,000 people in nearly 400 hotels across the UK.

Refugee groups have called the plan "completely inadequate", while councillors from the local area - which is popular with tourists - have opposed the proposals.

Home Secretary Suella Braverman and Immigration Minister Robert Jenrick have both been instrumental in the plans.

Prime Minister Rishi Sunak said they would save taxpayer money and reduce pressure on hotels, adding: "It's part of our broader plan to stop the boats."

"It can't be right" that the country is spending so much on housing migrants in hotels, the PM told reporters in Peterborough.

Just under 4,000 people have arrived on the south coast so far this year after crossing the Channel in small boats.

On Wednesday evening 41 migrants in two boats were taken back to France after getting into difficulty in the Channel. Several other boats made it half way across and those on board were taken to Dover by the Border Force.

The use of the Bibby Stockholm will mark the first time that migrants are housed in a berthed vessel in the UK.

The Home Office said it was in discussion with other ports and further vessels would be announced "in due course".

Charities and local councillors have opposed the plans, with the Refugee Council saying the barge will be "completely inadequate" to house "vulnerable people".

"A floating barge does not provide what they need nor the respect, dignity and support they deserve," said chief executive Enver Solomon.

Amnesty International called for the plans to be abandoned, and said use of the barge to house migrants was a "ministerial cruelty".

Dorset Council said it had "serious reservations" about the suitability of Portland Port as a location, adding: "We remain opposed to the proposals."

The British Red Cross said that docked barges did not "offer the supportive environment that people coping with the trauma of having to flee their homes need".

Christina Marriott, the charity's executive director of strategy and communications, called for a "more effective and compassionate asylum system" that would help people integrate into a community.

Mr Drax, whose constituency includes Portland, told BBC News on Tuesday he was "very concerned" about the impact on the area which "relies on small businesses".

This comes weeks after the government announced plans to tackle small boat crossings through the Illegal Immigration Bill.

The legislation would mean anyone found to have entered the country illegally would not only be removed from the UK within 28 days, but also be blocked from returning or claiming British citizenship in future.

Bill Reeves, chief executive of Portland Port, said he encouraged "everyone in the community to approach this with an open mind", adding that during the vessel's preparation there would be close ties with the local community and voluntary groups.

Portland, where Bibby Stockholm will be docked, was also once home to a prison ship. It closed in 2006 after criticism from the Chief Inspector for Prisoners who said inmates had no exercise and no access to fresh air.

Meanwhile, Labour criticised the plans, with shadow home secretary Yvette Cooper calling the announcement a sign of the government's "failure to clear the asylum backlog".

She said: "This barge is in addition to hotels, not instead of them, and is still more than twice as expensive as normal asylum accommodation."

Liberal Democrats home affairs spokesperson MP Alistair Carmichael said the barge was a symbol of "the government's failed asylum policy".