The Metropolitan Police Service (MPS) made repeated attempts to silence a whistleblower who exposed the widespread manipulation of crime statistics, it has emerged.

Documents seen by the Guardian show that senior officers made three separate attempts to stop PC James Patrick speaking out over the course of less than five months. In one letter, they went so far as to insist he be barred from having any contact with any member of the public.

He was sent two further letters within a few days this month warning him about interviews he intended to do with the BBC. He was told he faced further disciplinary action if he continued to speak out. He was eventually referred to the directorate of professional standards after he did the interviews, in which he said the Met "puts reputation before the truth".

As a result of Patrick's evidence to the public administration select committee, the head of HM Inspectorate of Constabulary Tom Winsor admitted that the manipulation of crime figures was taking place. The UK Statistics Authority withdrew the Met's gold standard national statistics status.

The Met commissioner, Sir Bernard Hogan-Howe, was forced to admit the numbers were being fiddled and said the issue was a cause for concern.

Bernard Jenkin, the chair of the parliamentary committee that investigated the manipulation of crime stats, said: "The most depressing part of our inquiry is the way in which the Metropolitan police have treated my constituent, PC James Patrick, who was our key witness."

He also called for an overhaul of the protections offered to whistleblowers and ministers are considering a host of "radical" proposals, including anonymity and protection from misconduct proceedings.

In the first letter to Patrick, dated 25 November 2013, Commander Allan Gibson of the Met's directorate of professional standards (DPS) wrote: "I need to remind you that you are currently subject to restrictions which include 'not having contact with the public'. As such you are prohibited from having contact with the media or its representatives and should not give interviews whilst subject to the current restrictions to duty.

"I also take this opportunity to remind you that you are also subject to a restriction not to engage in blogging or access any social network sites whilst on police duty. It should be noted that breach of restrictions to duty is a very serious matter which could result in further disciplinary action."

The subsequent letters set out the force's media policy, reminding Patrick that he must be given permission by senior officers before speaking to the media, which Patrick did not get.

Following the interviews with BBC Radio 5 Live and the One Show, the third letter informed Patrick that he had been referred to the DPS.

The news follows MPs' demands that the police watchdog open an investigation into Patrick's treatment at the hands of the force.

It has also emerged that the Met is forcing Patrick, who is claiming constructive dismissal at employment tribunal, to go without pay for months. The MPs say the forces should be barred from withdrawing "interim relief", which is normally available to people bringing such cases while their hearings are in process.

When he announced his resignation last month, Patrick insisted that he felt he had no choice but to leave because of his treatment at the hands of senior officers.

He said: "This resignation arises directly from my treatment as a result of making disclosures in good faith and in the public interest.

"My experience led me to see just how flawed the whistleblowing system is, how it fails, but also to firmly believe that no police officer should normally resign or retire while subject to any misconduct investigation. But the circumstances are such that I have no choice."

A Met spokesman confirmed that Patrick "was written to regarding what appeared to be ongoing breaches of MPS policy".