David Letterman becomes the latest big name to walk away from a US institution - and late-night TV here just won't be the same

Out of America: For more than two decades Letterman and his great rival Jay Leno, who retired in 2014, competed. Between them, they embodied the genre

Jay Leno, left, hosted by David Letterman on The Tonight Show in 1979 (NBC Universal)

For those of us who believe that life, politics and celebrity should be presented as comedy with a dash of hot pepper, these are sad times. A few weeks ago, Jon Stewart announced that he was stepping down as host of The Daily Show, a satirical take on US news, especially politics, which is often more accurate than the real thing.

That was bad enough, but only the first part of a double whammy. On Wednesday, David Letterman – master of deadpan goofiness and peerless connoisseur of the absurdity of human existence – is stepping down from The Late Show. For 33 years, Letterman has been a fixture on late-night TV, first at NBC and then CBS. Since the retirement of his rival Jay Leno, Letterman has ruled the late-night universe.

It’s a peculiarly American entertainment genre, a five-nights-a week mix of comedic monologue and chat show, featuring famous guests and bizarre antics, lubricated by a studio orchestra that is an actor in the plot. But the key ingredient is the host, in the case of Leno and Letterman a bigger star than all but a handful of those invited to appear.

In the US, late-night TV means precisely that. It runs from 11.30pm until 2am. Letterman and Leno have been opening acts followed by even later shows – and woe betide anyone who meddles with the scheduling. A few years ago, Leno wanted to move to a 10pm prime-time slot. For all his popularity, the experiment bombed.

These days, talk is the cheapest form of TV programming. Oddly, though, the American format doesn’t travel, not even really to Britain. Back in the 1970s, Michael Parkinson apparently wanted to launch a show modelled on The Tonight Show Starring Johnny Carson. Carson, inspiration of both Letterman and Leno, had by then turned late-night TV into a national institution, but the BBC governors didn’t want to know. “Too American,” they complained.

Too vulgar as well, they might have added. But, with a few exceptions, notably news programming and historical dramas such as Wolf Hall, British TV these days is no more upmarket than its transatlantic counterpart. Resistance has accordingly softened; the chat show, hosted first by Jonathan Ross and now Graham Norton in the BBC’s prestigious Friday-night slot, is bearer of the late-night standard.

Instead, a reverse takeover is under way. If American-style chat is making only slow inroads in Britain, British and foreign hosts are marching into the US – from John Oliver, Stewart’s former sidekick on The Daily Show, who now has his own Last Week Tonight show on the HBO channel, to James Corden on CBS’s The Late Late Show, which follows Letterman. An invader’s success, however, is not guaranteed. (Just ask Piers Morgan.)

True, the number tuning in has dropped to a third of the 12 million who watched Carson in his heyday. But, in today’s atomised TV universe, when you can record a programme for later viewing or catch bits on a mobile app, even four million represents a decent rating. Indeed, Americans’ fondness for late-night TV is one reason, a University of Pennsylvania study found, that so many people get less than the recommended eight hours of sleep.

And, for all their silliness and potential banana-skin moments, the late shows are beloved by politicians. After a true clunker of a speech at the 1988 Democratic nominating convention, Bill Clinton turned to Johnny Carson and The Tonight Show for redemption. Four years later, when he was running for president himself, Clinton appeared on another late show, hosted by Arsenio Hall, in which he wore dark glasses spoofing Elvis, and played “Heartbreak Hotel” on the saxophone.

How demeaning for a would-be leader of the free world, the purists fretted. But historians now credit the Elvis moment with helping to reignite Clinton’s then stalled campaign, opening the path that would lead him to the White House. That’s why Barack Obama and even David Cameron have been guests of Letterman – proof that politicians, too, are human beings.

A subtler propellant for late-night TV has been the rivalry between Leno and Letterman. The latter was Carson’s chosen successor when he stepped down in 1992; instead NBC gave the job to Leno, and a deeply upset Letterman decamped to CBS. For more than two decades, they competed, until Leno retired in 2014. Between them, they embodied the genre. Leno, broadcasting from Los Angeles, was the laid-back master of the one-liner. Letterman, born in Indiana but implanted in New York, was edgier and zanier, inventor of such routines as the Stupid Pet Trick and the Stupid Human Trick (sample: a girl who played violin on a pogo stick). His audience laughed at them, but Letterman’s most endearing ability was to laugh at himself.

He called himself “a towering mass of Lutheran Midwestern guilt”, and made a habit of revealing his own travails and disasters to his audience. After undergoing emergency heart surgery, he had the nurses and doctors who saved him on the show to thank them. And then there was the scarcely believable blackmail affair.

Even on air, Letterman was a flirt. In 1995, Drew Barrymore famously bared her breasts to him (her back to the audience), and in 2014, Tina Fey partially disrobed on set. But this was nothing compared with what happened in 2009, when Letterman told his amazed viewers that a fellow CBS employee was demanding $2m not to go public with details of Letterman’s bedding of various young female staffers. The charges were correct, Letterman admitted, even managing to extract self-humiliating comedy from his shame.

All was quickly forgiven and forgotten. But now he’s going. CBS has not revealed the line-up for Letterman’s last night on Wednesday. What we do know is that his successor is Stephen Colbert, formerly Stewart’s partner in crime on The Daily Show. Colbert’s terrific. But, without David Letterman, late-night TV here just won’t be the same.