A Whitehall brainstorming session prompted by Priti Patel led to the idea being floated of sending asylum seekers to a volcanic island in the South Atlantic, the Guardian understands.
The Financial Times reported that the home secretary had asked officials to look into the idea of processing asylum seekers on Ascension Island, an isolated volcanic British territory, and on St Helena, which is part of the same island group but 800 miles away.
However, according to Home Office sources, the proposal only arose after Patel sought advice on how other countries deal with asylum applications. Australia, for example, keeps them on overseas islands while it processes claims.
The source said Patel asked the Foreign Office for ideas, and among those raised were “implausible ones” such as the use of Ascension or St Helena.
Patel is expected to address the issue of Channel crossings by migrants in a speech to the Conservative party conference on Sunday, and has repeatedly vowed to stop those arriving in the country by boat.
Watch: Migrants make off at speed as dinghy lands at Kent beach
She has called on the Royal Navy to help tackle the growing number of small boats and appointed a former Royal Marine, Dan O’Mahoney, to the role of “clandestine Channel threat commander”.
In August she said the number of crossings was “appalling and unacceptably high”, adding: “I am working to make this route unviable.”
The UK is dealing with record levels of arrivals across the Channel, and – according to PA Media analysis – nearly 7,000 people have landed in the UK by small boats this year.
New plans drawn up by the Home Office show that people could be housed in a detention centre criticised for inhumane conditions, and Conservative MPs in Kent have raised concerns about the housing of migrants in nearby hotels and army barracks.
Ascension Island, which has a population of less than 1,000, is home to a Royal Air Force station and was used extensively as a staging point by the British military during the Falklands conflict in 1982.
St Helena is also one of the most isolated islands in the world, lying 1,210 miles off the west coast of Africa.
It is part of the British Overseas Territory of St Helena, Ascension and Tristan da Cunha.
Watch: Migrants intercepted as they journey across channel
A Home Office source said: “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.
“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.”
Nick Thomas-Symonds, the shadow home secretary, said: “This ludicrous idea is inhumane, completely impractical and wildly expensive. So it seems entirely plausible this Tory government came up with it.”