A veteran television beauty, Selina Scott, is taking Five to an employment tribunal under the new law banning “ageism”. It seems that the TV channel asked her about filling in for Natasha Kaplinsky's maternity leave, but after “initial discussion” she was not offered the gig, and a younger woman was.

Well, never mind the ageism, or indeed the dangerous inadvisability of making yourself known as a) 57 years old and b) litigious (who's going to approach her now?). What seems sorrowfully clear is that whatever the tribunal decides, Ms Scott has fallen victim to a far more familiar, and more irritating, quirk of media life: the Availability Check.

It works like this. A media organisation - TV, radio, sometimes advertising - wants to fill a role. Someone halfway up the tree decides to curry favour by presenting their boss with a tempting choice, rather in the manner of a boutique hotel waitress smiling over a basket of varied muffins. So they call half a dozen freelances, gushing about how they'd love to have them on board and asking them all to “keep the dates! I'll be back”.

The muffins duly block off the dates and wait. For most of them, nothing happens. Someone else gets the job and, in the excitement, the putative employer often forgets to call back to release the date. The muffin rings up, shyly, to be met with: “Who? Oh, I see. No, that was just an availability check.”

Sometimes, you can do a whole pilot programme and be startled six months later to hear its familiar theme tune and somebody else saying hello. Nobody told you. Jobbing builders wouldn't put up with this sort of treatment, but, tragically, mid-rank and new-fledged broadcasters often do.

Once, years ago, I was asked to book a fortnight's leave from being a Today presenter to film a TV project. No contract appeared, and on the verge of messing up my whole year's holidays, I rang to check. A baffled PA said: “Didn't he tell you? We got XX to do it, it's really exciting.”

I have no axe to grind these days: I have plenty of work and am quite lazy. Also, I learnt long ago that the only answer to the weaselling rudeness of the “availability check” is: “Right now the date's free. Call again if you make your mind up. But I'm saving nothing.”

Still, it is satisfying to think that from now on, arrogant media managers will be running scared that the whole muffin basket will leap up and sue them for discrimination on age, race, sexuality or disability.

Serve them right. They can try the old-fashioned expedient of making a list and working down from the top until someone says yes, then booking them.

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