Ministers are understood to be considering converting disused ferries moored off the coast to process people seeking asylum in the UK.
Record numbers of people crossed the Channel to the UK in small boats last month, despite Home Secretary Priti Patel vowing to stop to the crossings.
Labour called the proposal to process people on ferries “unconscionable”.
But Downing Street has said it is looking at what other countries do “to inform a plan for the UK.”
Home Secretary Priti Patel asked officials to look at policies including housing people who are seeking asylum offshore.
On Tuesday, the Financial Times reported the Foreign Office had carried out an assessment for Ascension Island, a remote UK territory in the Atlantic Ocean – which included the practicalities of transferring migrants thousands of miles – and decided not to proceed.
Now the Times reports that the government is giving “serious consideration” to the idea of buying retired ferries and converting them into processing centres, but it says the Home Office rejected a proposal to use decommissioned oil platforms in the North Sea.
The paper also says processing migrants on an island off the coast of Scotland had been considered, but First Minister Nicola Sturgeon tweeted that “any proposal to treat human beings like cattle in a holding pen will be met with the strongest possible opposition from me”.
Asked about the story on ITV’s Peston show, International Trade Secretary Liz Truss said “I’m not going to comment on leaks from government. We do have a serious issue with illegal migration, and I’m always 100% behind the home secretary on that issue.”
Nearly 7,000 people have reached the UK in more than 500 small boats this year.
By 23 September, 1,892 migrants had arrived during the month, more than in all of 2019.
Labour’s shadow home secretary Nick Thomas-Symonds said Labour would oppose any move to use ferries, adding: “Even considering this is appalling.”
Conservative MP for Gravesham in Kent, Adam Holloway, said the Home Office was “completely right” to be looking at other options that were “some sort of deterrent” for asylum seekers.
He told Radio 4’s Today programme: “We need to break the link in people’s minds that if you get to Britain you’re going to stay in Britain, you’re going to stay in a hotel and you’re going to be accommodated.”
He added that the UK needed to find a “civilised version” of the model used by Australia, which has controversially used offshore processing and detention centres for asylum seekers since the 1980s.
A Home Office source said this week that ministers were looking at “every option that can stop small boat crossings and fix the asylum system”.
“The UK has a long and proud history of offering refuge to those who need protection. Tens of thousands of people have rebuilt their lives in the UK and we will continue to provide safe and legal routes in the future,” they said.
“As ministers have said we are developing plans to reform policies and laws around illegal migration and asylum to ensure we are able to provide protection to those who need it, while preventing abuse of the system and the criminality associated with it.”
No final decisions have been made.
To be eligible for asylum in the UK, applicants must prove they cannot return to their home country because they fear persecution due to their race, religion, nationality, political opinion, gender identity or sexual orientation.
A caseworker decides if they have a valid claim by taking into account factors such as the country of origin of the asylum seeker or evidence of discrimination.
This is supposed to be done in six months but delays in processing claims have increased significantly in the last year.
While waiting for a decision to be made, asylum seekers are usually not allowed to work and are initially placed in hostel-type accommodation before longer-term housing is arranged.