The prime minister declined to say where they will be moored, but said they will have the capacity for an extra one thousand migrants who enter the UK illegally.

The government has already acquired one ship, the Bibby Stockholm, which will be used to provide accommodation for around 500 male asylum seekers off the Dorset coast.

Politics Live: Sunak claims small boats plan 'starting to work';

Speaking at a news conference in Kent about his "stop the boats" plan, Mr Sunak said this will dock in Portland within a fortnight and two more barges had been secured.

The prime minister said: "To reduce pressures on local communities we will also house people on ships. The first will arrive in Portland in the next fortnight and we've secured another two today."

On top of this measure, Mr Sunak said thousands of extra spaces for migrants have been found in hotels by making people share rooms.

The prime minister insisted this was "more than fair" following protests outside accommodation in Pimlico, London.

He said: "If you're coming here illegally claiming sanctuary from death, torture or persecution, then you should be willing to share a taxpayer funded hotel room in central London."

Charities and opposition MPs have previously criticised the plan to house migrants in barges, saying the government should focus on reducing the backlog of asylum seeker applications to reduce reliance on expensive hotels.

Labour leader Sir Keir Starmer also said the government needed to secure more returns agreements,

But Mr Sunak, who has staked his premiership on reducing Channel crossings, said the number of journeys were down by around a fifth since last year and insisted "our plan is starting to work".

He said the returns deal with Albania had led to 1,800 people being sent back, and was having a deterrent effect, with the number of people arriving illegally from that country down by "almost 90%".

Mr Sunak said: "Before I launched my plan in December, the number entering the UK illegally in small boats had more than quadrupled in two years. Some said this problem was insoluble, or just a fact of 21st century life.

"They'd lost faith in politicians to put in the hard yards to do something about it. And of course, we still have a long way to go. But in the five months since I launched the plan, crossings are now down 20% compared to last year.

"This is the first time since this problem began that arrivals between January and May have fallen compared to the year before."

Mr Sunak also defended the inclusion of children in new detention rules, claiming that to exempt them would create an "incentive" for smugglers to put more young people on boats.

He went onto suggest that the UK was doing better than other European countries to tackle illegal migration, but said that the government was not "complacent".

He said preparations are being put in place so that once legal challenges are complete "we have more detention capacity to hold those who arrive illegally, enough court capacity to process their cases and the planes to remove them".

"With grit and determination, the government can fix this and we are using every tool at our disposal."

The speech comes after polling found the majority of the British public think the prime minister is failing on his five priorities, which include stopping small boat crossings.

Sir Keir said the promise of further measures to tackle the crisis was "like Groundhog Day".

He told reporters in Somerset: "We need to stop the boats. We're clear we don't want anyone making that dangerous journey.

"But all we've had from the government is policies that aren't working, then the reannouncement of the same policy, with a self-congratulatory pat on the back. It feels like groundhog day and it's costing the taxpayer a fortune."