Department says helping vessels acts as ‘pull factor’ but rights groups say escaping war and famine is more likely motive

The Home Office has defended its decision to end British support for search-and-rescue operations for migrants in danger of drowning in the Mediterranean, after criticism that it marked an ethical nadir for Britain.

A statement said the decision agreed by the home secretary, Theresa May, with other European interior ministers this month had been taken because the rescue operations, which had so far saved the lives of more than 150,000 migrants, were acting as a “pull factor” for illegal migration.

“Ministers across Europe have expressed concerns that search-and-rescue operations in the Mediterranean … [are] encouraging people to make dangerous crossings in the expectation of rescue. This has led to more deaths as traffickers have exploited the situation using boats that are unfit to make the crossing,” the statement said.

But Amnesty International’s UK director, Kate Allen, denied that saving lives was a pull factor and said history would judge May’s decision as unforgiveable. “This is a very dark day for the moral standing of the UK. When the hour came, the UK turned its back on despairing people and left them to drown.”

Allen said that the Italian navy’s “desperately needed” search-and-rescue operation in the Mediterranean had saved thousands of lives and other European countries should be stepping up to share that responsibility with them, not shirking it.

“The vague prospect of rescue has never been the incentive. War, poverty and persecution are what make desperate people take terrible risks. History will judge this decision as unforgiveable,” she said.

The shadow home secretary, Yvette Cooper, said: “Home Office ministers seem to be saying that European countries should deliberately turn our backs on those whose lives and safety are at risk in order to set an example for others. That’s never been the British way. We should be working with other countries to renew efforts to stop people attempting this dangerous journey in the first place, not calling on everyone to stand aside and let men, women and children drown.”

Sarah Teather, the former Liberal Democrat minister for children and families and chair of the all-party group on refugees, also strongly condemned May’s decision. “This decision is deeply depressing,” she said. “We would rather let people drown for nothing other than baseless political motives. It shows that when it comes to immigration, the government has plumbed new depths of inhumanity.”

Teather said that it was no use pretending the problem had nothing to do with Britain and “to wash our hands as people died”. She said that the attempt to turn Europe into a fortress, with no safe routes in, was forcing migrants to risk their lives. “We are forcing people to choose between dying in their own war-torn country and drowning in the sea.”

A Home Office spokesperson confirmed that May backed the decision at the last EU justice and home affairs council, when the decision was taken to bring to an end the existing Italian-led search-and-rescue operation called Mare Nostrum.

It is to be replaced with a much more limited EU “border protection” operation codenamed Triton run by Frontex, the EU’s external border agency, which will operate within 30 miles of the Italian coast and will not conduct search-and-rescue missions.

However, the Italian navy said yesterdayon Tuesday that it will continue the Mare Nostrum search-and-rescue mission because no order has so far been received from the Italian government to stop.

Admiral Filippo Maria Foffi, the navy’s commander-in-chief, told a conference in Brussels that the Italian navy had no intention of standing down, and hinted at a division within the Italian government on the issue.

Mare Nostrum received around €30m (£24m) from the European commission after the Lampedusa tragedy in 2013, although no further funding applications have so far been received from Rome.

Human rights organisations have raised fears that more migrants and refugees will die in their attempt to reach Europe from the north African coast. The hard-pressed Italian navy will be left to mount what search-and-rescue operations it can. The new European operation will have only a third of the resources of the Italian operation that is being phased out.

British policy was quietly spelled out in a recent House of Lords written answer by the new Foreign Office minister, Lady Anelay: “We do not support planned search-and rescue operations in the Mediterranean,” she said, adding that the government believed there was “an unintended ‘pull factor’, encouraging more migrants to attempt the dangerous sea crossing and thereby leading to more tragic and unnecessary deaths”.

Anelay said: “The government believes the most effective way to prevent refugees and migrants attempting this dangerous crossing is to focus our attention on countries of origin and transit, as well as taking steps to fight the people-smugglers who wilfully put lives at risk by packing migrants into unseaworthy boats.”

The Home Office told the Guardian the government was not taking part in Operation Triton at present beyond providing one “debriefer” – a single immigration officer – to gather intelligence about the migrants who continue to make the dangerous journey to Italy.

Other EU countries have responded to the call for help with two fixed-wing aircraft and three patrol vessels.