Celebrity endorsement is nothing new. A quick search of Wikipedia reveals even Pope Leo XIII and Queen Victoria were at it as far back as the 19th century. In their cases it was testimonials to heighten interest in patent medicines.

It was probably Band Aid in 1984 which first harnessed the power of celebrity on a mass scale to highlight a particular cause. And since then, charities have become ever more sophisticated in getting their message to a wide audience by tapping into society’s obsession with celebrity.

Breakfast is frequently offered a famous name using their A-list status to draw attention to others less fortunate than themselves. Many of those offers are politely declined but some do end up on the sofa, as did the British-born Hollywood actress Sienna Miller. She’d been to India to highlight the issue of global warming and was interviewed by us, Radio Four’s Today and BBC News 24 as she encouraged society to think about the environment.

Nobody is pretending that her opinion is worth more than others but that doesn’t mean I’m not interested in what she has to say. She wasn’t gifted six minutes of BBC One air time to preach on the social injustices of climate change.

In fact, she had to defend why we should listen to her opinion and were her actions of flying to India hypocritical, actually increasing her carbon footprint.

On Breakfast, Bill and Kate challenged her repeatedly on her beliefs; she gave an illuminating, insider’s description of how Hollywood, a major, global industry, was adjusting the way it operates in response to concerns over the environmental threat to our planet.

You can’t escape from the fact that Sienna is one of our most in-demand actresses. This doesn’t give her automatic and unchallenged access to our viewers but it does make her well placed to outline the movie industry’s reactions to a worldwide phenomenon.

There’s one personality amongst Catherine Tate’s menagerie of characters with which I can most closely relate. Thankfully I’m not talking about Lauren the cheeky teenager but the awkward party guest who can’t help but put her foot into it - usually in spectacular and toe-curling fashion.

As always, observational comedy is at its best when it’s accurate and so to 9.09am on Friday morning as the eloquent and debonair Rupert Everett graced the Breakfast sofa to talk about the paperback release of his autobiography Red Carpets and Other Banana Skins.

Like Catherine Tate’s caricature, Rupert surprised our viewers with a comment that at best can be described as startling, and at worst, lewd. In response to an innocuous question from Susanna Reid about how Julie Andrews’ Oscar winning performance as Mary Poppins first lured him into showbusiness, he unfortunately described how, until he’d seen the quintessential English nanny, he’d thought rural cinemas were places where you were able to become intimate with your girlfriend.

I’m not going to spell out here exactly what he said (it won’t take you long to find it in its colourful glory elsewhere on the ‘net) but needless to say some of those watching weren’t best pleased that the actor who can currently be heard as the voice of Prince Charming in the latest child-orientated Shrek film felt the need to be so graphic on morning television. And Susanna and co-presenter Charlie Stayt are to be commended on their appropriate reactions and swift on air apology.

Daily, I mentally applaud the bravery of the guests which we subject to live television. We don’t quite have the smell of the greasepaint and the roar of the crowd, but certainly with the knowledge that there are millions of people watching, the madness of the moment can sometimes get the better of even the most seasoned of performers.

I am convinced that this is what happened with our Hollywood star.

Were his comments inappropriate? Certainly. Were they deliberate? Certainly not. I greeted him as he came off air and I was struck by two things. Firstly, he looked much taller in real life and secondly he was mortified by his slip of the tongue. He walked into the corridor with a hand framing either side of his unshaven face. “I can’t believe I said that,” he apologised. “I am so sorry, it just slipped out”.

The abnormality of conversation under the watchful gaze of millions of viewers had, in my opinion, tripped Mr Everett, a man who makes a living from saying other people’s words. He visually flinches as soon as he makes his childhood recollection and I’ve no doubt his apology once he’d come off air was sincere. There is one thing I am sure of. You can’t get a more innocent question than one which features Mary Poppins and Julie Andrews and this won’t be the last time a guest shocks us on live television.