A Whitehall whistleblower has claimed the Justice Secretary, Chris Grayling, has ordered advisers to vet all answers given by his department to official parliamentary questions to ensure a "favourable reply" is provided.
In a letter to shadow justice secretary Sadiq Khan MP, the "concerned official" claims Ministry of Justice (MoJ) staff at all levels are "infuriated" by the way the minister's advisers have sought to drag them into "the spin machine".
Mr Khan has written to MoJ permanent secretary Ursula Brennan to demand an investigation into the allegations made by the whistleblower and has accused Mr Grayling of politicising the department.
The shadow justice secretary and MP for Tooting has also called for a review of parliamentary answers given to him in recent months, which he says have shown a "noticeable deterioration" in timeliness and quality.
An MoJ spokeswoman said it is committed to answering parliamentary questions "in a way that provides the necessary context for members".
Mr Khan said: " It appears as if I am being deliberately denied information I am entitled to.
"The only explanation is that Chris Grayling wants to hide how badly he is doing as Justice Secretary."
He went on: "Asking parliamentary questions is absolutely crucial to MPs. Without them, it would be almost impossible to get to the bottom of what's really happening in the justice system, what taxpayers money is being spent on and whether the Government's policies are succeeding or failing.
"If my answers are being manipulated for party political purposes, the public are denied the true facts.
"This is bad for democracy and bad for the British public."
The shadow justice secretary labelled the Justice Secretary a "cowboy" and attacked his record at the Department for Work and Pensions (DWP).
He added: "That's why I'm demanding an immediate inquiry by the most senior officials to get to the bottom of whether the Ministry of Justice is being blatantly politicised with MPs being denied information we are entitled to with obstacles put in our way.
"Information must be freely available, quickly, with no grubby interference by a political spin operation trying to hide the embarrassment of Chris Grayling."
MoJ officials preparing answers to parliamentary questions have been told to pay "particular interest" to questions in 48 areas, including prisoners in police cells, first-class rail travel, deaths in custody and ministers' personal matters, the whistleblower claimed.
In his letter to the permanent secretary, Mr Khan said parliamentary answers go unanswered, some are dealt with via holding answers, which fail to be followed up, and some provide answers to different questions.
Among unanswered questions, issues such as prison capacity and the experience of staff at Oakwood prison run by G4S are covered, some of which Mr Khan says are "clearly politically embarrassing" for the Justice Secretary.
An MoJ spokeswoman said: " Special advisers are employed to provide advice and assistance to ministers across a wide range of areas, as required and in line with the code of conduct for special advisers.
"The MoJ receives a high volume of parliamentary questions on a wide range of subjects.
"These vary in complexity, and can sometimes involve compiling detailed statistical information. We are committed to answering PQs in a way that provides the necessary context for members."