It is important to understand why Sir Michael Fallon is no longer secretary of state for defence. He went not because he placed an uninvited hand on the knee of a female journalist at a boozy party conference dinner 15 years ago. Julia Hartley-Brewer, the target of his unwanted advances, says that losing his seat in the cabinet would be a “ridiculous” penalty for that. Anyone with an IQ in double figures can twig that this is not why he quit. Nor did he go because he made a lewd remark to Angela Leadsom, though it didn’t help his cause when she brought this complaint to the prime minister’s inner circle when they were debating his fate. According to the most convincing accounts of the events that led to his departure, the prime minister had come to her own conclusion that he couldn’t remain in office. As she writes in the Observer today, the journalist Jane Merrick had been in touch with the prime minister’s office shortly before he quit, to tell them that Sir Michael had “lunged at” her.

So I’m doubtful whether “resign” is the correct word for his departure. This has the smell of a sacking dressed up to look like a resignation. There’s a clue in the cool tone of the letters that he exchanged with Theresa May. He expressed his “utmost admiration” for the armed forces and pledged to “support the government”; he said not a word in esteem of the prime minister and made no promise to continue to support her personally. He had not responded to Ms Merrick’s account at the time of writing. He has says other accusations against him are false.

The removal of her defence secretary suggests that Mrs May has a better appreciation of the seriousness of the storm over sexual harassment and abuse that now swirls around Westminster than some of her colleagues. When the “Weinstein effect” first began to blow through London SW1, the response of some of its denizens was to contend that there was no legitimate reason for anyone to get outraged. It was even, in some quarters, being treated as a bit of a giggle. “Kneegate”, they chortled. Getting a proper focus on the meaning of this moment hasn’t been helped by the “spreadsheet of shame” that has done the rounds. This lists allegations of assault and behaviour that are nasty but not illegal and conflates those with tittle-tattle about consensual relationships and the sexual peccadilloes of some parliamentarians. The appellation “Palace of Pestminster” trivialises. “Sexminster” won’t do either. This is not an old-fashioned “sex scandal” of the type that felled Tory ministers during Sir John Major’s time at Number 10, when the tabloids exposed their relationships with women who were not their wives.

The gravest accusation has come from a Labour activist. Bex Bailey says she was raped at the age of 19 by a senior colleague at a party event and told by another party official not to report it. No party is unstained and the leaders of both the main parties are under pressure. Kelvin Hopkins, a veteran comrade of Jeremy Corbyn, has been suspended while there is an investigation of complaints about his conduct. Mr Corbyn has yet to explain why he had Mr Hopkins, who admits to sending a suggestive text to a woman nearly five decades younger, but denies everything else, in the shadow cabinet in spite of warnings about the sexual harassment claim against him.

This is trouble for all the parties, but the fallout will be almost certainly more consequential for the government because it is the government. The more so because, before this storm broke, it was already an extremely brittle and riven government. Two more of Mrs May’s ministers – Mark Garnier and Damian Green – are being investigated by the Cabinet Office. It is especially nightmarish for her that one of them is Mr Green, her de facto deputy, the chairman of a host of key cabinet committees, one of her oldest friends in politics and someone she has depended on very heavily since she lost her majority at the election.

Mr Green has been instrumental in keeping the May show just about on the road. He denies inappropriate behaviour towards a much younger woman and has tooled up with libel lawyers. His case will be investigated by Sue Gray, the director general of propriety and ethics at the Cabinet Office. Ms Gray has enormous experience – she was there for the expenses scandal – and has a high reputation. But to the outside world it will look mighty strange that a civil servant who works at the Cabinet Office is investigating the politician who is in charge of the Cabinet Office. Once again, we are faced with the ancient question, which parliament has often struggled with and never satisfactorily resolved, of who polices the politicians, who judges the lawmakers. It is true that abuses of power can and do happen in any kind of workplace, not just Hollywood and Westminster. What makes politics and showbusiness different is that both are trades in which there is an extremely high premium on personal connections and patronage. This greatly amplifies the opportunities for abusers to exploit power imbalances. MPs operate like small businesses, employers in their own right, in charge of the hiring and firing of their own staff. Those staff, very often people with their own political ambitions, are frequently much younger than the employers who can make or break careers. Safeguards for staff that have become a routine part of the company architecture in businesses do not exist at Westminster.

That structural defect is compounded by a cultural one. When confronted with scandal, the first impulse of politics is to hush it up. Ms Bailey says she was told to keep quiet on the grounds that pursuing her case would damage her career. Victims of sexual harassment, abuse and assault have been encouraged to stay silent because going public will hurt the tribe. Political parties are not incentivised to root out and deal with bad conduct within their own ranks. The clannish instinct is to cover up rather than give ammunition to opponents and the media. This has contributed to an environment in which sexual predators and bullies think they can behave disgustingly – in the most serious cases, criminally – and get away with it.

It is now well known that the Tory whips used to keep “a little black book”, in which were detailed the character defects of their MPs. Labour whips did much the same. Information is power in politics and personal information can be the most potent weapon of all. Secrets are a valuable currency at Westminster. Knowledge of misconduct could be used to coerce parliamentarians to vote the way their leaders wanted them to vote. It was sometimes – to use plain language – a tool of political blackmail. Both parties will insist that this practice doesn’t go on any more, but it remains the case that whips often know things about MPs that the parliamentarians wouldn’t want to have to explain either to their families or in front of a television camera. This is useful leverage and the more so when the parliamentary arithmetic is as precarious as it is today. It is a tool parties will not gladly relinquish, but whips cannot go on being enforcers of loyalty and keepers of secrets at the same time as supposedly being a sort of human resources department.

A helpline for abused or harassed staff has already been announced. New codes of conduct are being written. Mrs May will meet other party leaders tomorrow to discuss further action. All have an incentive to deal with this before it becomes any more corrosive to the reputation of parliament. There is now great pressure to establish a mechanism, independent of partisan and self-interested party meddling, for dealing with complaints about sexual predation and bullying. This will only work if victims can have confidence in it.

Loads of new rules won’t be worth much unless they are accompanied by a determination to enforce them. The most important thing to look for is a cultural shift in which abusive behaviour is no longer tolerated and hushed up, but faced and dealt with. Mrs May could be the right woman at the right time in the right office to lead that. From what I know of this prime minister, she will have a visceral disgust of predatory men who prey on younger people. She first made her name telling her fellow Tories that they had to stop being “the nasty party”. Her immediate responses have drawn compliments from unexpected quarters. Harriet Harman, Labour’s former deputy leader, does not lightly praise a Tory. She has commended Mrs May for being robust. The prime minister’s best instincts will be with Ruth Davidson, the Tory leader in Scotland, when she declares that they must “clean out the stables”.

This would be easier advice to follow if Mrs May was a stronger prime minister. Her desire to do the right thing will be in contention with the brittle context in which she is operating. More revelations and more resignations will threaten further destabilisation of an already fragile and factionalised government. It could make a weak leader even weaker. Not acting will run exactly the same risk. Mrs May should follow her best instincts. If she needs to swing the axe again, she ought to do so.