Which of the following stories sounds true to you? Lily Cole claims to be able to move chairs through mental will power. Kate Perry sucked Russell Brand's face off. Pixie Geldof puts sweets into her bra.

The first story appears on the Popbitch website. The second on the TMZ website. The third was invented by the film-maker Chris Atkins to test how far tabloid journalists will go in search of intrusive information. The hoaxing of the red tops has been turned into a documentary film, Starsuckers.

Reporters were offered stories about celebrities checking into cosmetic surgery clinics. In a secretly recorded conversation, a Sunday Mirror journalist explained the process involved in buying a story: "You put [the information] in front of the editor and you say... it is going to cost us this much money if we are going to run the story. What do you reckon?"

Things must have changed since the days Andy Coulson was editor of the News of the World. When he gave evidence about phone tapping to a House of Commons committee, he told them he was too busy to inquire into the provenance of stories.

My two questions are: how can red tops possibly know what is true and not true in the great tide of celebrity stories, and, how much does it matter?

The two routes to celebrities are through maximum control agents and the vigilant public on their mobile phones. This is the see-saw of celebrity news. A star is at one moment being reverently wheeled out as the latest Unicef ambassador, and the next, filmed stumbling out of an S and M club.

The public assumes celebrities lead double lives and have their own split responses to them. The Leona Lewis fan delivered what Florence and the Machine might call a kiss with a fist. The line between reality and unreality is easily mistaken.

George Clooney is right to question with innocent lucidity why journalists would print trivia they know to be untrue, but how could you possibly verify private details about celebrities without tapping their phones?

Much celebrity journalism seems designed to boost sales or careers. I assume that most of what I read in the red tops is a collusion between agents and journalists. I have no idea if a single word written about Jordan is based on fact.

In the absence of hard evidence, papers resort to picture-based speculation. We know that celebrities must work harder on maintenance than civilians, as Liz Hurley calls us. At some point we are going to snap them coming out of a Harley Street clinic in dark glasses.

Celebrity cosmetic surgery is a whole journalistic genre of its own. There are breast operations and liposuction and if in doubt you can accuse almost everybody of botox. Attaching cosmetic surgery to celebrities is like looking into MPs' expenses; you are bound to find something.

Personally, I think the Starsuckers crew lost plausibility when they suggested Ricky Gervais had undergone a nose job and Hugh Grant liposuction. But it would be strange if a member of a girl band were not having something done to her breasts. It has what Richard Ingrams called "the ring of truth".

I would be worried if journalists started lying about the national debt, but in the arena of journotainment everybody appears to be in on the act – the newspaper, the celebrity, the public.

As the small boy in the balloon-adventure-that-never-was story said to his family on national television: "You guys said that we do this for the show." What I would like to know from Starsuckers is, just who is hoaxing whom?