After Donald Trump’s long-serving lawyer Michael Cohen agreed a plea deal with federal prosecutors in a financial crimes case against him, members of the president’s inner circle fear he could be about to “flip”.

Doing so would see Cohen definitively turn against his former employer to cooperate with FBI investigators pursuing the question of Russian election hacking in exchange for more lenient sentencing in December.

Once so loyal to Mr Trump he pledged to “take a bullet” for him, Cohen admitted in court in New York that he had attempted to pay “hush money” to former Playboy bunny Karen McDougal and adult film actress Stormy Daniels “at the direction of the candidate” after the women alleged they had had affairs with the billionaire property tycoon prior to his candidacy.

The charges against Cohen resulted from FBI special counsel Robert Mueller’s ongoing probe into the Trump camp’s alleged ties to associates of Russian president Vladimir Putin and the possibility the Kremlin might have tried to influence the outcome of the 2016 presidential election.

What else he might be able to divulge about the private dealings of the reality TV star he served so unquestioningly for 10 years is a tantalising prospect.

“Flipping”, in which a member of an organisation turns state’s witness against their former allies for personal gain, has a history as old as Judas and is typically the last resort of desperate men.

While a whistleblower like biochemist Jeffrey Wigand might inform on research tampering in the tobacco industry as a matter of principle, more often than not, those persuaded to flip are doing so to save their own skins when they know the game is up.

Derided as turncoats, squealers and snitches by their former friends, flippers boxed into a corner and encouraged to leak information on their criminal cohorts frequently face great personal risk as a result and are forced to enter witness protection programmes.

Organised crime has provided plenty of engaging characters who have ratted on their fellow wise guys, none more famous than Henry Hill, the New York mobster and Lucchese family associate whose evidence resulted in 50 convictions in 1980 and whose memoir provided the basis for Martin Scorsese’s celebrated gangster film Goodfellas (1990).

Another case was that of Joseph Valachi, who testified before the US Senate in 1963, becoming the first to admit the existence of the Italian-America mafia, detailing its infrastructure and hierarchy and in so doing breaking the “omerta” or code of silence Cosa Nostra members are sworn to.

Valachi said he was motivated to come forward in a spirit of public service but may also have feared for his life as a result of receiving the “kiss of death” from mob boss Vito Genovese.

While Valachi was a low-level “soldier”, others to cooperate with the Justice Department like Jimmy Fratianno have been much more senior.

A Los Angeles crime lord implicated in the car bombing of a rival, ”Jimmy the Weasel”, who was himself suspected of playing a role in the assassination of John F Kennedy and carried out five known murders, testified about his knowledge of organised crime in America and the role of Florida gangster Santo Trafficante Jr in a CIA plot to take out Cuban leader Fidel Castro in the 1960s.

​Fratianno was subsequently booted out of witness protection for publishing two memoirs and promoting himself as a celebrity criminal.

Another boss to turn stool pigeon was Salvatore “Sammy the Bull” Gravano, a Gambino crime family boss whose evidence as an FBI witness brought down the notorious John Gotti in 1991.

Some other highlights from the underworld include Leroy “Nicky” Barnes, known as “Mr Untouchable”, who turned on his Harlem heroin ring The Council and gave up 109 names in 1983, including his own wife.

That same year saw gambler Ken Eto, “Tokyo Joe” to his friends, surrender the honour of being the highest-ranking Asian American in the Chicago Outfit to spill the beans after one too many attempts on his life.

Finally, there’s New Jersey boss Vincent Palermo, supposedly the inspiration for Tony Soprano, who told on the DeCavalcante family in 1999 in exchange for leniency after admitting to the murders of reporter George Weiss and rival Louis LaRasso. He later entered witness protection and, of course, ran a strip club.

Turning to the history books, Nazi general Dietrich von Choltitz might be considered a flipper for his refusal to obey Adolf Hitler’s order that he level the city of Paris under German occupation, realising this would be a crime against culture and instead surrendered to the Free French in 1944.

Flipping goes with the territory in the spying game. Double agents like Aldrich Ames, Kim Philby and Juan Pujol Garcia AKA “Garbo” all changed sides at opportune moments to the embarrassment and consternation of their employers.

Liberal Party MP Peter Bessell is another famous flipper, turning against his old friend and party leader Jeremy Thorpe in 1970 over the Norman Scott affair. As shown in the recent BBC dramatisation A Very English Scandal, Pessell was once a trusted confidant of Thorpe but was persuaded to appear as a prosecution witness in his trial at the Old Bailey for plotting his former lover’s murder.

The prospect of flipping was a source of much paranoia among paramilitaries during the Troubles. The likes of Christopher Black, Joseph Bennett and Kevin McGrady all came forward to name names and expose domestic terrorism in 1983.

More recently, Birmingham drug trafficker Constantine Michael Michael deserves a special mention.

Trump's presidency: US media reacts to Manafort and Cohen convictions Show all 16 1 /16 Trump's presidency: US media reacts to Manafort and Cohen convictions Trump's presidency: US media reacts to Manafort and Cohen convictions New York Post Trump's presidency: US media reacts to Manafort and Cohen convictions The Washington Post Trump's presidency: US media reacts to Manafort and Cohen convictions Newsday Trump's presidency: US media reacts to Manafort and Cohen convictions St Louis Post Dispatch Trump's presidency: US media reacts to Manafort and Cohen convictions Chicago Sun Times Trump's presidency: US media reacts to Manafort and Cohen convictions The Star Ledger Trump's presidency: US media reacts to Manafort and Cohen convictions Daily News Trump's presidency: US media reacts to Manafort and Cohen convictions The New York Times Trump's presidency: US media reacts to Manafort and Cohen convictions San Francisco Chronicle Trump's presidency: US media reacts to Manafort and Cohen convictions The Boston Globe Trump's presidency: US media reacts to Manafort and Cohen convictions Houston Chronicle Trump's presidency: US media reacts to Manafort and Cohen convictions Miami Herald Trump's presidency: US media reacts to Manafort and Cohen convictions Detroit Free Press Trump's presidency: US media reacts to Manafort and Cohen convictions The Wall Street Journal Trump's presidency: US media reacts to Manafort and Cohen convictions The Dallas Morning News Trump's presidency: US media reacts to Manafort and Cohen convictions USA Today

On the surface, Michael appeared to be a legitimate businessman operating a string of lucrative saunas and massage parlours. In truth, he was both a major importer of cocaine and cannabis from mainland Europe and a “supergrass”, informing on his acquaintances to the police between 1989 and 2001.

Under the strain of paranoia exacerbated by an increasingly out-of-control coke habit, Michael was eventually arrested and sentenced to six years in prison but not before providing information that led to 49 arrests, 34 convictions and the dismantling of 26 drugs gangs. His mum, his wife and his girlfriend were among the names given up.

Donald Trump is not the only world leader currently living in fear of being betrayed.

Israeli prime minister Benjamin Netanyahu is facing a corruption investigation and has seen close advisers Nir Hefetz, Shlomo Filber and Ari Harow all agree to turn state’s witness and testify against him.