Louis Theroux, the BBC interviewer whose subversive style has disarmed so many of his subjects, has been visibly rattled by one of his "victim", the PR supremo Max Clifford.Millions of viewers will see the normally unflappable journalist who jealously guards his private life on the back foot during his latest documentary, to be broadcast on Tuesday night.
The alarm on his face is first seen when he realises Clifford was planting stories about him in the newspapers while the BBC2 documentary was being made.
Clifford made stricter demands for privacy from the programme makers that any previous subject - to protect the deals he brokers daily for a list of celebrity clients including Pop Idol judge Simon Cowell.
He set out with a mission to give Theroux a taste of his own medicine, vowing from the outset of the programme that he would "fight back" if Theroux "took liberties" with him.
After accompanying Clifford on a night out at a London lap-dancing club, ostensibly for Cowell to meet the Mirror's 3am girls, its dawns on Theroux that Clifford has set him up.
The Mirror hacks are there to get a story on Theroux, having had their previous requests for interviews turned down.
Later Clifford pulls the same trick on Theroux with the Guardian's Simon Hattenstone - who was also snubbed by the BBC man - in an elaborate set-up at a Sainsbury's supermarket in Weybridge that goes embarrassingly wrong.
When Theroux challenges Clifford about the stories being published about him, Clifford replies: "You were looking very uncomfortable. The biter gets bit."
He goes on to explain his own personal game of semantics to the miffed Theroux: "If you had said to me at the beginning, 'Could you keep me out of the papers?', I could have done, but you never did."
To say the two did not take to each other would be an understatement. The executive producer of the show, David Mortimer, said the two "are not pally", but denied relationships ended on a sour note.
Throughout the film there are pregnant pauses when Theroux and Clifford stare each other out hoping the other will crack first. And for all his scheming, it is Clifford that finally does.
He blows his top in the Weybridge Sainsbury's after Theroux refuses to play ball after overhearing Clifford and Hattenstone talking about the set-up after assuring him there was none.
"If I'd known you were going to be silly about it, you can all fuck off," storms Clifford, ripping off his mic. "Let's call it a day and let me get on with my shopping and doing what I do."
Theroux didn't uncover anything about Clifford that we didn't already know: that he lies as a living and is happy to admit to it, earning thousands of pounds attracting publicity when it is wanted and repelling it when it is not. He admits on screen that he charges clients £10,000 a month.
But the most revealing thing in the latest "When Louis Met..." documentary, is the extent to which Theroux doesn't like the boot being on the other foot.
Mr Mortimer, the producer, said: "We realised this might happen with Max. Louis didn't feel threatened by [the stories about him in the press], but he was slightly annoyed by it.
"He understands there is interest in who he is but that doesn't necessarily mean he has to agree to go into great depth about his private life."
Mr Mortimer said there were plans for a new Theroux show with him tackling foreign and sometimes unknown subjects as well as continuing with British celebrities.
When Louis Met ... Keith Harris and Orville in Panto attracted just 2.4m viewers this week, nearly 1 million fewer than tuned in to watch last week's encounter with the former boxer Chris Eubank.
When Louis Met Max Clifford will be screened on BBC2 on March 26 at 9pm.
