Plans to send people who enter the UK on small boats to a volcanic island in the south Atlantic are being considered in Whitehall, a government minister has confirmed. On Monday, the Home Office minister Sarah Dines said the proposal to send people to Ascension Island could replace the government’s plan to deport people to Rwanda, should that policy fail. “We are pretty confident that Rwanda is a legal policy. The high court and the lord chief justice found that it was, so that is what we are focusing on. But, like any responsible government, we look at additional measures. So we are looking at everything to make sure our policy works,” she told Times Radio. While the high court did rule the policy was legal, the court of appeal has since ruled it is not. The government has indicated it will seek a final decision in the supreme court – the highest in the country. Dines added: “We need to reduce the pull factor of illegal criminal gangs getting people to this country, basically abusing the system.” Pressed on the potentially high cost of sending refugees 4,000 miles to be processed, Dines said the focus continued to be on delivering the agreement with Rwanda, but that ministers were looking at “every other additional measure, as you would expect”. Later on Monday, Rishi Sunak’s spokesperson said the Rwanda removal scheme remained “the right approach to progress”. It is understood that fresh advice about the Ascension Island plan was sought within the Home Office after the current government was formed last October. There have not been any recent or active discussions about the policy, suggesting it remains a hollow threat. However, ministers have yet to formally kill it off – meaning talk of the plan will continue. The Ascension Island idea was suggested in Whitehall three years ago at the request of the then home secretary, Priti Patel. The Financial Times reported that she had asked officials to look into the idea, while a Home Office source later told the Guardian it was suggested to her after she sought advice on how other countries dealt with asylum applications. However, under the original policy, people whose asylum claims were accepted as genuine would have had the possibility of returning to the UK. But now under the government’s Illegal Migration Act any person deemed to have tried to enter the UK through irregular means will be permanently excluded from coming back. In 2020, the plan was also described as “implausible” by a Home Office source. Jacob Rees-Mogg, who was a cabinet minister when the plans were first considered, said the idea was dropped because “it was just thought to be impossibly expensive to do”. He told GB News: “I was involved in some of the discussions looking at this whilst I was a member of the government and unfortunately it would cost at least a million pounds per person you sent there to do it. “You’ve got to send out Portakabin residences for your builders, then you’ve got builders who have to live there whilst they’re doing the building, then you have to build the premises for the migrants to live in, then you’ve got to persuade people that they want to go and live on Ascension Island for long periods to run the centre.” Asked why it was being considered again, Dines told Sky News: “Well, times change … This crisis in the Channel is urgent, we need to look at all possibilities and that is what we are doing.” For years, however, the Conservative government has ignored advice from humanitarian groups and refugee and asylum experts, who have said the way to reduce the number of attempted crossings is to offer alternative “safe and legal” routes to the UK to claim asylum. Labour hit out at the “Groundhog Day” briefings about people being flown to Ascension Island. Yvette Cooper, the shadow home secretary, called the latest briefings the “same headline-chasing” as 2020. She said other mooted plans – such as pushbacks and wave machines to stop the boats – were “unworkable” but ministers continued to talk them up as a possibility. Dines’s comments came as it was revealed that an immigration detention centre close to Gatwick was two-thirds empty due to a shortage of Home Office staff to work there. A report from HM’s chief inspector of prisons showed that the capacity at Tinsley House immigration removal centre was 162 but there were just 50 detainees there at the time of the inspection due to “staff shortages among the onsite Home Office team”. While the report found the centre was generally well-run, concerns were raised about cases of torture and other vulnerabilities. The report was published soon after the Illegal Migration Act passed into law. A key plank of the new act is to significantly increase immigration detention.