The following correction was printed in the Guardian's Corrections and clarifications column, Monday 2 November 2009

The story below about the origins of Pop Idol and the TV programmes it inspired said that in 2001 Simon Fuller and Simon Cowell met Alan Boyd, who was then head of Thames TV, and "rattled through their idea for an ambitious new show to identify an unknown British singing star". To clarify: Simon Fuller is credited as the creator of Pop Idol. As we said in our story, Simon Cowell is not one of the owners of the programme's format.

On Tuesday 13 February 2001 TV veteran Alan Boyd saw two men he had never met before in his London office and the meeting changed the face of Saturday night entertainment.

Nothing about the then head of Thames TV's meeting with two Simons suggested that television history was in the making, or that he and his production team were about to benefit from an enormous stroke of luck. As Mr Cowell and Mr Fuller rattled through their idea for an ambitious new show to identify an unknown British singing star, Boyd scribbled notes on two sides of jotting paper during the hour-long meeting.

On a piece of Pearson-headed notepaper (Pearson then owned Thames), Boyd sketched the original idea for Your Idol, the working title for a show that became a seminal reality/entertainment format once on air that autumn. Pop Idol, as it became, attracted mass family audiences, sold around the world, produced instant No 1 chart hits, and was so successful that it spawned derivatives including The X Factor, American Idol and Britain's Got Talent.

It would also act as a template for a host of new shows set to transform Saturday night entertainment, with a mixture of live judging and public voting all in the initial pitch. Ranging from Strictly Come Dancing to Dancing on Ice, these shows have combined to give a massive financial and reputational boost to the British television production sector at home and abroad.

Lavish production

Pop Idol still runs in 44 countries nearly nine years on, while the American Idol version is sold on to 150 territories. The X Factor, Cowell's breakaway hit following his split with Fuller a year later, sells in 16 countries and his Got Talent format is made in 25 national versions.

No one knows the combined monetary value of Pop Idol, American Idol and the other Cowell shows because the revenues are widely shared. Thames, now renamed Fremantle, and owned by RTL, still owns one third of the Pop Idol format, and oversees licensed productions including the Cowell formats. Fuller's 19 company, which controls two thirds of the Pop Idol format, also takes big cuts. Total profits are estimated to run into hundreds of millions of pounds.

The original idea, which had been inspired by talent shows such as Popstars, included national auditions on a scale never before attempted, a panel of four judges, public voting, with the result declared live, big auditoriums, lavish production and state of the art sets and lighting.

Boyd scribbled down the key points, now familiar to audiences around the world, on the memo paper we print here for the first time, which he usually keeps carefully squirrelled away in his desk drawer. The details are fascinating and reveal, for example, that the backing of the Sun newspaper was seen as vital to the success of the show; the team even considering approaching Dominic Mohan, the then editor of the paper's Bizarre column and now its editor, to be a judge. In the event, only one other former Bizarre editor, Piers Morgan, has enjoyed a role in the Got Talent spin-off.

Despite the global success of the show Boyd, who had made his name with popular hits including Surprise Surprise, Blankety Blank, Blind Date and the Royal Variety Shows, recalls being only modestly interested.

"Was I excited? No. I thought, these two boys know what they are talking about. I saw them as the engine, me as the carriage."

Boyd's role was to supply the television talent and experience to turn an idea into a hit show. It was not the work of market research, he points out: "This was not the product of a strategy meeting, it was experience and instinct."

After the meeting a small team worked with the originators on a 40-page production "bible", to flesh out the concept, and the cost, before pitching it to two broadcasters, the BBC and ITV.

Boyd admits: "We had no idea how many people would vote, and we didn't really think about texting." Boyd, who had joined BBC light entertainment in 1962, believes that the two Simons specifically came to see him because he had also overseen the first ITV charity telethons, in the late 1980s, which encouraged mass phone voting. The phone line scandal hit talent shows but not as much as other entertainment or competitions.

One of his trusted production experts, Richard Holloway, became the executive producer of Pop Idol (and subsequently of all Cowell's shows). The format was pitched to Lorraine Heggessey, then the controller of BBC1, who wanted to make it in-house. David Liddiment and Claudia Rosencrantz at the ITV Network said yes to the concept instantly. The X Factor is still a hit ITV1 show.

Instant feedback

Boyd, 68, who retired three years ago, remains a special adviser to RTL's chief executive Gerhard Zeiler, the owner of Fremantle. He also acts as an unofficial adviser to Holloway as he spends Saturday evenings watching The X Factor, and telephones with instant feedback.

He has started to pass on his experience to young producers at RTL-owned companies. His tips include avoiding copycat shows, keeping it authentic, getting the casting right with lots of personalities and heroes, and incorporating emotion.

"Big emotional moments" make a show, he believes. "Pop Idol changed from a singing contest to a story show when Gareth Gates stood before the panel of judges, and stuttered, before singing like an angel.

"In Big Brother people went into the house and started playing the game. Viewers immediately thought, this is false, and it no longer worked. It doesn't mean reality TV is dead." He does, however, offer his advice on what he sees as one of the hardest and most enduring dilemmas for those in charge of entertainment shows – how to say no to your biggest talent.

"You have to say no carefully," Boyd says. He is far too diplomatic to elaborate any further. But industry analysts have suggested that the current X Factor series is too over-produced after Cowell abruptly demanded big venue auditions, with full backing tracks.

Very few shows, however engaging, or well made, last forever. Channel 4, after all, is ditching its once iconic series, Big Brother, in 2010, after 11 years. And Cowell has already hinted about stepping back.

But The X Factor is in its seventh series and showing no outward signs of decay. Rosencrantz – one of the original Pop Idol producers, now at Virgin Media – says: "It is stronger than ever. It used to beat Strictly Come Dancing only in profile, never volume. Now it beats Strictly by a mile – but Strictly is very weak this series – with very very poor bookings. I think it [The X Factor] will go on as long as people have an appetite for the panel. It is panto – a show all about the panel!"

Some 10.7 million are tuning in every Saturday night, up from 9.2 million last year, despite the overlap with Strictly. On 18 October, 14.8m of us watched, half the television audience, better than last year's final's figure, 14.6 million. That really has the X Factor.