The top civil servant at the Home Office has said “all options are on the table” for the migration system, in response to reports officials were asked to consider proposals to hold refugees in offshore detention centres, including remote islands in the south Atlantic. Matthew Rycroft, the department’s permanent secretary, said the Cabinet Office would lead an inquiry into the leak of documents that revealed officials were asked to consider “possible options for negotiating an offshore asylum processing facility similar to the Australian model in Papua New Guinea and Nauru”. The documents, summarising advice from Foreign Office officials, include cost estimates of building asylum detention camps on the islands of Ascension and St Helena, as well as proposals to build facilities in Moldova, Morocco and Papua New Guinea. Appearing before the public accounts committee, a clearly agitated Rycroft said he would not comment on the content of leaks, adding “the civil service is here to give ministers impartial, fearless, honest, expert, independent advice and that is what we do. The system works when we do this in private.” Pressed by the chair of the committee, Meg Hillier, on whether transporting asylum seekers to Ascension Island was a “serious idea”, Rycroft said: “What I can confirm is the civil service has been responding to ministers’ questions about how other countries deal with what is a global issue – migration. “We have been leaving no stone unturned in doing that. We’ve been looked at what a whole host of other countries do in order to bring innovation into our own system.” He said no final proposals had been put to ministers and no decisions had been made. “This is in the realm of the brainstorming stage of a future policy. As ministers have said in the house, everything is on the table and so it should be at this stage in the process.” He said the aim of the exercise was “improving our system of asylum so we can continue to provide protection to those who need it in accordance with our international obligations and to make sure the system is not being abused”. He said some of the proposals would involve “continuity” while others would be “very different”. Asked about reports in the Times that retired ferries were being considered for use as asylum processing centres, Rycroft replied: “The advice that has been, and will continue to come back, will cover all different aspects including the law, operational practicalities, financing, value for money, diplomatic issues, public engagement issues. All that needs to happen privately in order for the civil service to give ministers the best advice we can.” Questioned by the Scottish National party MP Stuart McDonald about the source of the leaks, Rycroft said the Cabinet Office would be investigating the leak and whether or not it was politically motivated.