Whether new Special Minister of State Mal Brough is under Australian Federal Police investigation or not — he says he’s heard nothing from the AFP about anything to do with the Peter Slipper business — he needn’t worry too much about it.

The history of scandals and investigations at the federal political level suggests that, between the AFP and the Commonwealth Director of Public Prosecutions, somehow there’s always a reason not to charge a politician or government figure. Some examples:

Mal Colston: The Quisling Quasimodo from Queensland was a long-term rorter of his travel expenses and in 1997 was eventually charged with 28 counts of fraud in relation to his parliamentary entitlements. But Colston then claimed he had cancer and had only months to live, so the Commonwealth Director of Public Prosecutions promptly dropped the charges. So pleased was Colston at this news that he immediately recovered and lived until 2003.

Gary Hardgrave, Ross Vasta and Andrew Laming: Three Queensland Liberal MPs were the subjected of an extended AFP investigation in 2007 over the use of their parliamentary printing allowances. Despite Vasta admitting to an “administrative error” and repaying nearly $24,000, the CDPP decided there wasn’t a “reasonable prospects of conviction for a criminal offence” although its statement seemed to imply that in the CDPP’s view there was a prima facie case against each of the MPs.

AWB: The greatest corruption scandal of recent decades in Australia — in which the National Party-linked Australian Wheat Board bribed Saddam Hussein with hundreds of millions of dollars right up to the eve of the invasion of Iraq — has yet to yield a single serious conviction. The AFP simply abandoned its investigation of the scandal, meaning no criminal prosecutions for this industrial-scale bribery have ever been brought. The Australian Securities and Investments Commission — notoriously, the biggest joke among Australian regulatory agencies — also abandoned its pursuit of two AWB officers. ASIC has so dragged its heels on the prosecution of former chairman Trevor Flugge and former executive Peter Geary that their trial on civil charges won’t begin until next month — nearly 18 years after Australian intelligence agencies first learnt of dodgy AWB dealings with Saddam.

Godwin Grech: The Treasury public servant who admitted to forging an email in an attempt to implicate Kevin Rudd and Wayne Swan in corruption was never charged in relation to the forgery. In 2010, Commonwealth Director of Public Prosecutions Chris Craigie SC issued a statement saying Grech wouldn’t be prosecuted, based on “public-interest factors” and “Mr Grech’s physical and mental health.” Indeed, Grech, who in 2012 wrote about how much he was looking forward to a successful Tony Abbott prime ministership under governor-general John Howard, did nicely out of the whole saga — in 2013, it was reported the forger had, remarkably, received a payout from Treasury.

Gillian Triggs and the Brandis job offer: According to evidence to a Senate committee by the president of the Human Rights Commission, Gillian Triggs, in February the head of the Attorney-General’s Department, Chris Moraitis, met with her to tell her the Attorney-General had lost confidence in her, that she should resign and that she’d be given another senior legal job, an international one, if she did so. This was a possible breach of s.142.1 of the Criminal Code, which makes it an offence to dishonestly offer to provide a benefit with the intent of influencing a Commonwealth public official in the exercise of their duties. Moraitis, asked to provide his notes for the meeting, claimed to have “lost” them. Invited by Labor to investigate the incident, the AFP declared that it could “not identify evidence to support the allegation” against its two most senior portfolio officers.

Bronwyn Bishop: Did the then-speaker misuse her travel entitlements? Don’t bother asking the AFP (which Labor did). While people who might have engaged in fraud can usually expect to face a police investigation, politicians are luckier — the AFP, while insisting it “has not refused to investigate allegations from the complaints”, did exactly that, referring Bishop’s case to the Department of Finance, headed by Jane “kids overboard” Halton, who had said the claims against Bishop were simply a case of sexism. And how’s the Finance investigation going? Oh, sorry, that’s secret — taxpayers can’t be told about the status of an investigation into whether an MP has misused their taxpayer-funded entitlements.

Peter Slipper: Finally, a winner! Long-term enthusiastic travel entitlement user Peter Slipper didn’t get the luxury of a Department of Finance investigation, but was investigated for fraud by the AFP the moment he stepped aside as speaker. Slipper, a serial repayer of entitlements he claimed to have accidentally spent on unofficial business, was prosecuted for fraud and found guilty last year of three charges of dishonesty. Except, wouldn’t you know it, Slipper appealed and had the convictions overturned, partly, the appeal judge said, because the prosecution had failed to disprove that Slipper’s infamous winery tour at taxpayer expense could have been for Slipper to get to know more about the wine industry, or maybe meet someone for parliamentary business.

Then, of course, there are the regular leaks from cabinet, from government departments, from intelligence and law enforcement agencies and from Senate inquiries, all serving the interests of particular individuals and agencies, which mysteriously are never investigated by the AFP despite being ostensible breaches of the law. It’s the genuine leaks, which only serve the interests of transparency, that get investigated.

Rest easy, Brough — neither the innocent nor the guilty have much to fear from the AFP and the CDPP.