LEADING Brexit campaigners Michael Gove and Boris Johnson have launched a stinging attack on David Cameron, describing his failed pledge to cut immigration as "corrosive of public trust".

The broadside, in a letter to the Sunday Times, put the issue of migration back at the centre of the EU referendum debate.

It followed a bruising week for the Leave campaign as the Remain side claimed to have won the economic argument for staying in the EU.

Pro-EU campaigners were further buoyed yesterday by a survey showing nine out of 10 economists believed Brexit would be damaging.

Mr Gove and Mr Johnson said the government's pledge to get migration below 100,000 was unachievable as long as Britain remained in the EU.

Official figures show net migration - the difference between the number of people coming to the UK for at least a year and those leaving - rose to 333,000 in 2015.

Net migration from the EU was 184,000.

In their open letter, Mr Johnson and Mr Gove said: "Voters were promised repeatedly at elections that net migration could be cut to tens of thousands.

"This promise is plainly not achievable as long as the UK is a member of the EU and the failure to keep it is corrosive of public trust in politics."

They also said they were "particularly concerned about the impact of free movement in the future on public services".

"Class sizes will raise and waiting lists will lengthen if we don't tackle free movement," they wrote.

Number 10 said the claims were "a transparent attempt to distract" from the "overwhelming" view of economists and business leaders that Brexit would be "disastrous" for jobs, prices and opportunities.

The clashes came amid growing turmoil

in Conservative ranks.

Backbench MPs Andrew Bridgen and Nadine Dorries, who support Brexit, warned Mr Cameron would face a leadership challenge after the June 23 referendum if Remain won by a narrow margin.

Mr Bridgen said up to 50 MPs were prepared to push for a no confidence vote in the Prime Minister.

However a number of senior pro-Leave MPs, including Liam Fox, Chris Grayling and Iain Duncan-Smith, poured cold water on the chances of a coup.

In other developments, Tony Blair, the former Labour Prime Minister, warned against leaving the UK, saying it would not solve migration problems and would create an "enormous economic problem" which would affect jobs and living standards.

Leading faith leaders and senior figures from across the main faith communities also backed the case for Britain remaining in the EU.

They stressed its role in building peace in Europe and how action at European level can more effectively tackle problems such as climate change.

The group included the Very Rev Dr Ian Bradley, of St Andrews University, the Kirk's ecumenical co-ordinator Fiona Buchanan and Mona Siddiqui, Professor of Islamic and Inter-Religious Studies at Edinburgh University.

Rowan Williams, the former Archbishop of Canterbury, was also among 37 signatories to an open letter.

SNP MP Hannah Bardell singled out the EU's digital single market initiative, as she campaigned for a Remain vote in Scotland.

The scheme, the Nationalists' business spokeswoman said, would boost small businesses.

"Central to the campaign for voting to remain in the EU is the overwhelming economic case," she said.

Her comments came as party activists took the streets in a "weekend of action" to campaign for a Remain vote.

Humza Yousaf, who heads the SNP in Europe campaign, accused both sides of "depressing scaremongering" but said "the positive, progressive case for the benefits is overwhelming".

The SNP stepped up its campaigning following criticism from some Remain allies who claimed the party's public attacks on David Cameron's economic case for the EU were helping the Leave side.

One SNP MP, Stephen Gethins, complained to Vote Leave after it quoted him on some of its campaign literature.