Image caption Tony Blair is one of five people to have made the front cover more than 50 times

Private Eye's front cover has been making fun of royals, politicians and celebrities for 50 years. In the age of the viral video and the mirthful meme, why is a defiantly old fashioned design still so popular?

It's home to the great, the good and the not so good. Margaret Thatcher has made 95 appearances, the Queen 62, while Jeffrey Archer and Saddam Hussein are both into double figures.

Private Eye is celebrating its 50th anniversary and it is the caption competition-style cover that sums up its satirical brand. The front cover is one of the most familiar sights on the shelves of British newsagents, glanced at by many more than the 200,000 people who actually buy the magazine.

The formula of headline, photograph and provocative speech bubble has rarely changed over the years. A selection of the best covers will be celebrated in a 50th anniversary book published this week, and at an exhibition starting at the Victoria & Albert Museum next month.

There have been many notable examples, including George W Bush under the headline "Bush: Countdown to War", intoning "10, 9, 8, 9, 5, 7, 2, er", or Adolf Hitler dressed in Nazi uniform, announcing "I've come as Prince Harry".

It's an effective way of getting across a joke, says the satirist John O'Farrell, who edits the topical comedy website News Biscuit.

For most people the magazine had crossed a line - it dared to suggest that people were being emotionally indulgent Satirist John O'Farrell, On controversial Princess Diana cover

"They were the first publication to have a photo on the cover and to put words in people's mouths." The formula has since been imitated for many years by the football magazine When Saturday Comes.

Guardian editor Alan Rusbridger applauds the do-it-yourself feel. "It's incredibly school magaziney but something it has never grown out of. That retro quality is part of its brilliance."

One he calls an early classic marked the death of apartheid South Africa's prime minister in September 1966. "Verwoerd: A nation mourns" showed a picture of Zulu tribesmen dancing. "It took the breath away at the time so completely disrespectful was it," notes Rusbridger.

Prime ministers are the most regular cover stars with Thatcher, Tony Blair and Harold Wilson the three most featured individuals.

A typically cruel example from April this year shows David Cameron talking to a patient in hospital, with both equipment and Nick Clegg in the background. The patient's speech bubble reads: "Watch out… there's a drip behind you." Cameron's response is "I know he's called Nick".

The cover is not just a brand identifier but a chance to boost sales, as shown by the issue following Rupert Murdoch's decision to close the News of the World. It used the headline Gotcha! - a reference to the Sun's notorious front page about the sinking of the Belgrano during the Falklands War.

Underneath there was a picture of Rebekah Brooks, Rupert and James Murdoch above a sub heading "Murdoch goes down with all hacks". The issue sold 250,000 copies, about 45,000 more than usual.

Image caption Right Royal treatment: The Queen has been on the front cover 62 times

The Sun's editor at the time of the Gotcha headline, Kelvin Mackenzie is a devoted reader of Private Eye despite being regularly lampooned by it during the 1980s.

He never held a grudge because "the stories about me were all true". They were also "bloody funny", he says.

Mackenzie loves the covers, citing the one after the English riots as a prime example. Under a headline "Olympic Rehearsal" there's a photograph of looters behind a burning car with one hooded youth saying to another "this is the worst opening ceremony ever".

There's a fearlessness to their satire that was best exemplified in the cover during the shocked aftermath of 9/11, Mackenzie says.

Under the headline "Bush Takes Charge" an official is pictured whispering in the ear of George W Bush. "It's Armageddon sir," reads the speech bubble. The president responds "Armageddon outahere!"

Editor Ian Hislop was criticised for insensitivity at the time. In Eye tradition, readers write in at such moments to say the magazine has gone too far and announce they are cancelling their subscriptions.

For Mackenzie such people misunderstand the magazine's business. "There are no limits. You know a cover like that is going to cause outrage but it's what people in advertising call your brand."

Image caption Private Eye is not only interested in domestic politics

Perhaps the most controversial cover in the magazine's history followed the death of Princess Diana. It showed crowds of mourners outside Buckingham Palace under the headline "Media to blame" with three speech bubbles coming out of figures in the crowd.

"The papers are a disgrace," says the first person. "Yes. I couldn't get one anywhere," says the next. "Borrow mine. It's got a picture of the car," says the third.

It was too strong for WHSmith, which banned the issue from its stores, causing the magazine to lose a substantial number of readers.

"For most people the magazine had crossed a line," recalls O'Farrell.

"It dared to suggest that people were being emotionally indulgent - both appalled by the media coverage and yet wanting to buy the car crash pullouts. Now we've woken up from our drunken reaction to Diana's death, a lot of people would say Private Eye got it right."

The cover is put together every other Monday by three people - Nick Newman, Hislop and his predecessor Richard Ingrams, who now edits the Oldie.

"Occasionally someone comes in with a fully formed idea like with the Gotcha one," says Newman. "But usually we'll bounce ideas off each other. We tend to give it half an hour then move on."

Image caption Everyone from sports stars to bankers can be awarded the Private Eye treatment

First they go through piles of pictures. Sometimes there's an obvious choice such as Obama and his security chiefs watching the raid on Osama Bin Laden's compound. But as Newman explains, they often like to give such an image an incongruous twist by mixing it with an unrelated news story.

So the picture of Obama and his staff was linked to the disastrous local election results for Nick Clegg. The cover shows Obama saying "That's horrible" while a military commander adds "It's a massacre" and an ashen-faced Hillary Clinton whispers "Oh my God, the poor Lib Dems".

Animals are often used as an amusing chorus.

One of Newman's favourite covers shows former Home Secretary David Blunkett and his guide dog beside a female police officer. The dog's speech bubble reads: "Watch out - he's on heat at the moment." The latest issue shows two sheep discussing the concreting over of the green belt.

Bad taste is not the only criticism levelled against the covers. Not all of them are riproaringly funny, such as the clunking effort from 1990 after Nelson Mandela's release from jail. "This is a black day for South Africa," says a speech bubble from prime minister FW de Klerk.

And the Independent's John Walsh has noted a "lurking homophobia", while former Labour deputy leader Roy Hattersley recently described the magazine as "public schoolboys laughing at the world outside the dormitory… at the expense of the peccadilloes and pretensions of lesser mortals".

Rusbridger, who is nicknamed Alan Rubbisher in the magazine, says they don't get everything right. "It operates in a strange no man's land between reporting and satire. Quite often they get things wrong."

But there's no point in getting cross, he says. The magazine dares to go where so many newspapers refuse to tread, in particular as a highly effective watchdog for the workings of the British press.

For Mackenzie, it's possible Hislop and his small team are the ultimate journalists. "All good journalists are outsiders. They're the ultimate because they're outside the outsiders."