Theresa May accused of trying to alter immigration report before Brexit vote

Theresa May faced accusations from within government that she tried to remove evidence about the positive impact of immigration on the British economy from a critical report that was published before the EU referendum.

Correspondence seen by the Guardian lays bare a six-month tussle between Conservative and Liberal Democrat advisers over the study, which was part of a government-wide exercise into the pros and cons of EU membership.

Emails dating back to 2014 show Lib Dem advisers, who were then in government as part of the coalition, complaining repeatedly about May’s interventions.

They claimed internally that the then home secretary was determined to paint a negative picture of Britain’s relationship with European countries when it came to immigration.The exchanges suggested that May wanted to claim that “benefits tourism” was a serious problem, attracting immigrants into Britain.

But the advisers said there was little evidence to support the assertion, suggesting instead that internal DWP figures might underline it as a “small-scale problem”.

“My impression is that Conservative secretaries of state are determined not to admit this,” wrote one participant. Another said: “The home secretary is also deeply committed to the argument that free movement allows foreign criminals into the UK.”

The suggestion will be seized on by pro-EU campaigners who believe that May made it harder for David Cameron to argue for Britain’s continued membership.

“A lot of the pro-free movement evidence has been removed,” complained one adviser, citing a UCL report that said eastern European migrants were “58% less likely to live in social housing” and one showing migrants paid more in tax then they take in benefits.

The emails report conversations among civil servants inside the Home Office and Department for Work and Pensions (DWP) saying that May had taken a particularly active interest in the study.

Overall, the Lib Dems expressed frustration at an attempt to depict free movement as a “one-way street”, with foreign workers using the UK’s NHS and claiming benefits, while downplaying the numbers of British people living and working on the continent.

The emails have been seen after Cameron’s former director of communications, Craig Oliver, accused May of repeatedly failing to throw her weight behind the campaign to keep Britain in the EU.

The report from the Home Office, with contributions from Ian Duncan Smith’s DWP, was one of the 32 Whitehall studies on the ”balance of competences” between the UK and the EU insisted on by the Conservatives in the 2010 Coalition Agreement.

The immigration report was the most bitterly contested and Nick Clegg, the former Lib Dem leader, has since publicly accused May of tampering with the report to minimise the number of British people living abroad.

But this set of emails goes further, suggesting the report was delayed because Lib Dems believed the home secretary’s office refused to release revised versions. They argued that the government would be left picking up the tab for Brits abroad if their interests were completely ignored.

Clegg’s party also described as “completely baseless” the idea that benefits were the key factor in attracting workers in the UK, rather than shortages of skills in the UK labour market.

Downing Street released the final report the day after parliament rose for the 2014 summer recess.

Lord Wallace of Saltaire, the Lib Dem minister who led the negotiations on these reports, told a similar story to the correspondence. “There was a deep-seated reluctance from within the home secretary’s office to admit that free movement brings benefits as well as costs to British citizens, or to allow us to cite evidence which weakened the Eurosceptic narrative,” he told the Guardian.

A source close to the prime minister accused the Lib Dems of trying “to rig the balance of competences review” and saying the country had since voted decisively to leave the EU.

“Theresa May has been completely consistent in her view that we need more control over our immigration system rather than less, and that levels of immigration are too high. Since becoming prime minister, she has made clear that following Brexit we will get the right deal to control the number of people who come to Britain from Europe,” he said.