Theresa May has buried bad news about Britain’s asylum system by delaying and manipulating the publication of independent inspection reports, the head of the Government’s immigration watchdog has warned MPs.

In a damning letter to the Public Accounts Committee, seen by The Independent, John Vine reveals that the Home Secretary is currently sitting on five reports believed to be critical of the Government, one of which was completed five months ago.

Mr Vine warns the MPs that the failure to publish his reports in a “timely” manner is “reducing their impact” and has “compromised” the independence of his role.

His letter, which comes just months after he announced he was stepping down early, raises serious questions about the extent to which Ms May’s is attempting to control critical stories about immigration in the run up to the election. It will also fuel suspicions that the Tories are unwilling to allow the publication of critical reports, after Norman Baker, the former Home Office minister, said the Government had suppressed reports on drug laws that would have contradicted their stance. The latest figures on immigration are to be published today. Tory MPs have been warned to expect net annual migration running at over 200,000 – twice its target.

Among the delayed inspectorate reports is one into a controversial operation to check the immigration status of anyone arrested in London which was given to Ms May in June. A report on visa over-stayers has also been delayed.

Border Force check the passports of passengers arriving at Gatwick Airport (Getty) (Getty Images)

The chair of the Public Accounts Committee, Margaret Hodge, accused Ms May of undermining Mr Vine’s “autonomy and therefore his credibility”.

In his letter, Mr Vine says that up until this year he had complete autonomy to decide when his reports, which cover all aspect of Britain’s asylum and immigration system, were published. This was the case under successive Home Secretaries since the post was established in 2008.

But Mr Vine said that in December last year he received a letter from Ms May saying that from then on, he would have to publish his reports through her department.

She claimed the change was because there had been a “misinterpretation” of the law by the Home Office

“I was concerned by these proposals for a number of reasons,” he wrote. “I feared, at the time it was made, that a consequence of her decision might be that reports would not be published promptly, reducing the impact of their findings.”

Mr Vine reveals he sought his own independent legal advice from Government solicitors, who concluded that the Home Office’s interpretation of the legislation was “neither the obvious nor the only interpretation of the law”.

But despite raising this with the Home Office his concerns were ignored.

Since the new system came into operation the Home Office has delayed the publication of 10 of his reports by up to four months each.

They have also “bundled” the publication of reports together which Mr Vine is understood to fear lessens their impact.

Shadow Home Secretary Yvette Cooper accused Theresa May of hiding (Getty) (Getty Images)

Allowing the Government to control the release date also allows ministers to release them at times when they will get little publicity – potentially burying unwelcome news.

In his letter to the PAC, Mr Vine makes it clear that he is unhappy. “Unfortunately my concerns have proven correct,” he writes.

“I consider that lengthy delays in publishing reports risk reducing the effectiveness of independent inspection, which depends to a large extent on timely publication of findings, and it is contributing to a sense that the independence of my role is being compromised.”

The letter could result in Ms May being called in front of Parliament to defend her position.

“It is simply not acceptable for the Home Secretary to decide when the Chief Inspector reports,” said Ms Hodge. “This inevitably undermines his autonomy and therefore his credibility.”

Yvette Cooper, the shadow Home Secretary, said: “It is shameful that the Home Secretary delayed the Immigration Inspector’s reports. Instead of hiding from a system in chaos, Theresa May should be putting it right.”

A Home Office spokesman said: “Publication arrangements have been brought into line with the 2007 legislation which requires the Home Office to lay the Independent Chief Inspector’s reports before Parliament. The legal advice was clear that the previous practice was not compliant with this legislation, and it is right that the department is adhering to the law and to parliamentary protocols.