The new prime minister should scrap the Tory commitment to cutting net migration to the tens of thousands, a report backed by two Conservative former immigration ministers has said.

Theresa May has remained committed to the target – which has never been reached – as home secretary and Prime Minister.

But with either Boris Johnson or Jeremy Hunt set to replace her next week, the Onward centre-right think tank said the 2010 target should be replaced with a detailed and long-term sustainable immigration plan.

The plan should include a commitment to reduce low and medium-skilled immigration over time.

A new Office for Migration Responsibility would act as a watchdog to monitor the Government’s record on the issue.

Communities Secretary James Brokenshire, who served as immigration minister under Mrs May in the Home Office, said: “It is right that, as we look to a positive future beyond Brexit, we look again at our approach to controlling migration and the targets we set.

“Immigration policy supports Britain’s continued success story as a growing economy.

“Changes in skills needs or workforce shortages mean that we need to continue to attract people to come to the UK and be part of this positive vision. But there is a need for balance.

“We have to do so in ways which recognise the cumulative pressures this can bring and the need for well integrated communities.”

Mark Harper, a former immigration minister who stood for the Tory leadership, said: “For far too long the public have thought, and quite rightly too, that our politicians do not have their hands on the wheel when it comes to immigration policy.

“This has to change, and as we leave the EU we will regain the ability to shape a migration policy that can control immigration from wherever in the world it comes.

“I hope that our next prime minister – whoever that may be – will welcome this report and embrace these proposals into their government’s agenda.”

Onward’s analysis shows that net migration to the UK would have been 1.4 million lower between 2010 and 2018 had the pledge introduced by David Cameron to reduce net migration to below 100,000 a year been met.

The think tank’s director, Will Tanner, said: “With net migration adding the equivalent of a city the size of Newcastle to the population each year, it is hardly surprising that the public no longer trust politicians on immigration.

“The tens of thousands target was once a powerful statement of intent but it has become a visible statement of failure.

“The next prime minister must replace it with a firm system that forces business and Whitehall to confront the trade-offs involved in immigration, and holds government’s feet to the fire for delivering on its pledges.”