Boris Johnson has defended proposals to send asylum seekers abroad to be processed, insisting that the policy was a “humanitarian one” intended to combat people smugglers.

The British overseas territory of Gibraltar and the Isle of Man are thought to be locations being considered by officials, under Home Secretary Priti Patel’s plans to overhaul the immigration system.

But Gibraltar’s government said it had not received any proposal on the issue from the UK, and chief minister Fabian Picardo has written to Ms Patel to say it will not happen.

Meanwhile, a spokesman for the Isle of Man Government said it had not been contacted by the UK Government and the crown dependency’s parliament is thought to be unlikely to approve any processing centre.

The plans to process asylum seekers abroad have drawn widespread criticism but when asked about the proposals, the Prime Minister insisted the objective was to “save life and avert human misery”.

“Because people are crossing the Channel who are being fooled, who are being conned, by gangsters, into paying huge sums of money, risking their lives,” he told a Downing Street press conference.

“People have died trying to make this crossing and it is a deeply repugnant traffic that we need to stop, and that’s why the Home Secretary has set out the tough series of proposals that you have seen.

“The objective is a humanitarian one and a humane one, which is to stop the abuse of these people by a bunch of traffickers and gangsters.”

Earlier on Thursday, Downing Street did not deny the Home Office is looking at proposals of using Gibraltar and other overseas territories to process asylum seekers.

In his letter to Ms Patel, Mr Picardo said there were constitutional and legal issues, as well as the “geographic limitations” of the territory which prevented it being used to process asylum seekers.

The chief minister said that while “we will not ever shirk our responsibility” to help Britain, “our geography makes some things difficult, however, and the processing of asylum seekers to the UK in Gibraltar would be one of them”.

“Immigration is an area of my responsibility as chief minister under the Gibraltar constitution and I can confirm that this issue has not been raised with me at any level,” he said.

“I would have made clear this is not area on which we believe we can assist the UK.”

Ms Patel has vowed to stop migrants making the perilous journey across the English Channel and is expected to publish details of plans overhauling the UK’s asylum and immigration system in the coming weeks.

The Times said plans due to be set out by the Home Secretary will include a consultation on changing the law so migrants seeking asylum can be sent to processing centres in third countries.

The Daily Mail suggested the plans would see migrants banned from claiming asylum in the UK if they had arrived from a safe country such as France, with their cases deemed “inadmissible”.

Those arriving in the UK via illegal routes would be removed to a third country – the newspaper reported Turkey was being considered – where they would remain until they could be repatriated, either to their home nation or the safe country they arrived from.

It comes after series of leaks last year suggested the UK Government was considering a number of offshore policies akin to those used in Australia.

These included sending asylum seekers to Ascension Island, more than 4,000 miles from the UK, to be processed, and turning disused ferries out at sea into processing centres.

Shadow home secretary Nick Thomas-Symonds said: “The Tories are lurching from one inhumane, ridiculous proposal to another.”

Bella Sankey, of the Detention Action charity, said: “Off-shore detention of traumatised people is ethically abhorrent and practically infeasible. It is totally unnecessary and would diminish Britain in the eyes of the world.”

The Government believes sending migrants to third countries for processing would be compliant with the European Convention on Human Rights (ECHR), according to reports.

The Times said the new legislation will include life sentences for people smugglers and the establishment of migrant reception centres on government land, with many currently being housed in hotels.

Ms Patel told MPs: “As we reform the asylum system, Global Britain will continue its proud tradition of providing safe haven to those in need through safe and legal routes.”

Her comments came in a written ministerial statement which said the UK had met a 2015 commitment to resettle 20,000 refugees fleeing the conflict in Syria.

She also announced £14 million of funding to help newly granted refugees to integrate in the UK, with pilot schemes to help them learn English, move into work, access housing and build links in their local communities.