A Home Office minister has urged that emergency rescue operations of drowning migrants trying to cross the Mediterranean “be stopped at the earliest possible opportunity” despite being told his approach amounted to “a barbaric abandonment of British values”.

The unrepentant immigration minister, James Brokenshire, was defending in public for the first time the decision taken by the home secretary, Theresa May, to refuse to support future search and rescue operations of migrants trying to cross the Mediterranean in rickety unseaworthy boats.

He insisted that the British government’s refusal to take part in future rescues and the ending of the current effort was essential because it was encouraging more migrants to make the journey and leading to further deaths.

But Brokenshire faced a growing barrage of criticism, with the official Labour spokesman telling him it was “a barbaric abandonment of British values”, and the former Liberal Democrat leader Lord Ashdown describing it as “discreditable”. There were also signs of unease among some Tory backbenchers, with James Lefroy demanding that rescue efforts should not be withdrawn before better help was put in place in north Africa to persuade would-be migrants not to flee.

An Italian navy operation, Mare Nostrum, has saved the lives of 150,000 migrants and refugees so far this year but despite their best efforts more than 3,000 have died. The Italian government has said the rescue operation is unsustainable and appealed to the European Union, including Britain, to take on the burden.

But May is believed to have been a leading figure among the European interior ministers who decided three weeks ago to only offer an EU border protection operation codenamed Triton, with a third of resources and a limited remit to patrol within 30 miles of the Italian coast. The first 40 miles of the journey from Tunisia will not be covered by their activities. Triton is due to be launched from Saturday when the Italian operation covering the whole width of the Mediterranean is due to start winding down.

Brokenshire was unrepentant in the Commons in defending the government’s approach, which was described by some Labour backbenchers as a policy of “let them drown”. He insisted that the Italian Mare Nostrum search and rescue mission had the unintended effect of placing more lives at risk by encouraging people traffickers to place migrants and refugees in more unseaworthy boats.

“Since Italy launched its Mare Nostrum operation in October 2013, there has been an unprecedented increase in illegal immigration across the Mediterranean and a four-fold increase in the deaths of those making that perilous journey.

“The operation has been drawn closer and closer to the Libyan shore, as traffickers have taken advantage of the situation by placing more vulnerable people in unseaworthy boats on the basis that they will be rescued and taken to Italy.

“But many are not rescued, which is why we believe that the operation is having the unintended consequence of placing more lives at risk.”

He said it was essential that these “emergency measures should be stopped at the earliest opportunity” and that their discontinuation be given the widest publicity in north Africa.

He insisted that the EU decision not to take over the Italian rescue operation had been unanimous among the 28 interior ministers earlier this month.

But his defence attracted the fiercest criticism from across all parties, with some MPs comparing it to turning back the Jewish “Exodus” refugee ships and the Kindertransport trains in the second world war.

Labour’s official spokeswoman, Diana Johnson, accused him leaving people to die in their thousands. She said he was willing to do anything to appear tough on immigration in order to face down the Ukip threat ahead of next month’s Rochester and Strood byelection. The Liberal Democrat Sarah Teather said he was “washing his hands of the problem – Pontius Pilate style”.

In the House of Lords, the former Lib Dem leader Lord Ashdown described it as “a discreditable policy” and warned that it might be illegal under international maritime laws.

But earlier Nick Clegg had sidestepped the issue, saying the decision to end the rescue operation was a matter for the Italians.