The man who was in charge of Britain's police until September has delivered a blistering attack on the "cancer" of corruption among a minority of officers as the crisis engulfing the service over the Andrew Mitchell "plebgate" affair reaches new heights.

Writing in the Observer, Nick Herbert, who quit as minister for police and criminal justice in David Cameron's autumn reshuffle, calls for urgent reforms to restore public trust, arguing that while "corruption may not be endemic, neither is it an aberration".

Herbert, while praising the "decent majority" of officers whom he says do "brilliant" work, suggests that for too long the police have been shielded from criticism by a lack of accountability and an unhealthily cosy relationship with sections of the press that rely on officers leaking "juicy" information.

In a sign of how Mitchell's resignation as chief whip in October, after he was accused of calling officers guarding the Downing Street gates "fucking plebs", is causing continuing bitterness and division in government, the ex-minister also has a sideswipe at cabinet secretary Sir Jeremy Heywood, implying that he failed to investigate the police claims thoroughly enough.

Mitchell admits that he swore at officers but denies using the word "plebs". He accused the officers of using "awful toxic phrases" and said police actions following his altercation were an attempt to "toxify" the Tory party as a whole. Mitchell believes he was the victim of a police stitch-up – a view reinforced after CCTV footage of the incident, released last week, appeared to contradict elements of the police account.

Herbert suggests Heywood failed to probe the evidence thoroughly. "The cabinet secretary's investigation of the incident, following hard on the heels of his green light to the flawed West Coast mainline franchise, has raised eyebrows," he says.

It is understood that Bernard Hogan-Howe, the Scotland Yard commissioner, cut short a holiday to be briefed on his force's investigation into whether its officers conspired to frame Mitchell.

On Saturday night, after unnamed "friends" of Mitchell accused Cameron of leaving Mitchell "swinging in the wind", Downing Street said the former chief whip had stepped down from his cabinet post because of lack of support in the Tory party, not a loss of backing from the prime minister.

Downing Street said Cameron had been shocked by recent disclosures about the events leading to Mitchell's resignation but challenged those who claimed Mitchell had felt let down at the time. "The prime minister stood behind his chief whip through weeks of growing demands to sack him," it said.

Herbert says the police must take stock following a number of disturbing revelations about their conduct, including the arrest last month of five detectives in Kent over allegations that crime figures had been manipulated, and the independent inquiry into the 1989 Hillsborough football disaster which uncovered a full-scale cover-up by South Yorkshire police.

He says elements within the police feel they can leak information to journalists. "Why is it that organisations like the Inland Revenue, which holds sensitive tax information on prominent figures, do not leak, yet police officers, with their powers of coercion and duty to uphold the law, think nothing of tipping off the press at the first opportunity?"

He adds that while the crisis in the police should not be exaggerated "the cancer must be cut out before it spreads". Reforms, including the introduction of elected police commissioners, must serve to hold the police more closely to account, he says.

The "plebgate" row is also threatening to tear apart the Police Federation, the organisation representing police interests. Senior members are known to be angry at the PR tactics deployed by its West Midlands branch as it sought to heap pressure on Mitchell, a local MP.

The West Midlands Police Federation employed the radio presenter and former Sun columnist Jon Gaunt to advise it on a campaign to protect its members from cutbacks. Its members were given media training and, once Plebgate erupted, they were issued with "PC Pleb" T-shirts that ensured the Mitchell row enjoyed sustained newspaper coverage.

In a stunt co-ordinated by Gaunt, whose PR company, Gaunt Brothers, lists the Sun newspaper, which broke the original Mitchell story, as a client, three senior members of the West Midlands federation met Mitchell at his Sutton Coldfield constituency office. The meeting was flagged to the press and the media scrum and ensuing interest heaped further pressure on Mitchell who resigned only days later.

On Saturday the national federation confirmed it was setting up an independent review of its structure because of "issues around the way it is able to lead and co-ordinate". The move is seen as a tacit admission that some federation members went too far in targeting Mitchell. The national chairman, Paul McKeever, says the body took "a very clear line" not to call for Mitchell's resignation.

However, in a press release issued days after the scandal broke, the federation quoted McKeever as saying: "It is hard to fathom how someone who holds the police in such contempt could be allowed to hold a public office."

The row has also heaped pressure on Hogan-Howe, who has publicly backed the two officers who were present when Mitchell attempted to leave through the Downing Street gate.

The home affairs select committee has written to the commissioner asking him to account for the Met's handling of the affair and is expected to question him on it early in the new year.

Mitchell is understood to be unhappy with what he considers an "unsatisfactory" exchange of letters between himself and Hogan-Howe, which has reportedly eroded his confidence in the commissioner.