IF anyone ever doubted the brilliance of the BBC, John Humphrys' interview with George Entwistle showed how excellent it still can be.

As the sabre-toothed tiger of the Today programme sank his fangs into his boss, and the listening millions stopped crunching toast so as not to miss a syllable, Humphrys used every weapon in the journalist's armoury. The result was a masterclass in how to get under someone's skin and reach the truth. In the space of 10 or 15 minutes, which no doubt felt to the Director-General like a lifetime, Humphrys was probing, dramatic, emotional, cool-headed and fearless. He blocked every bolt-hole and picked apart each excuse so that by the conclusion, like a frog under dissection, Mr Entwistle had been eviscerated.

It's to Mr Entwistle's credit that he neither lied nor blustered, and to Humphrys's that he knew when to dig deeper to provoke the humiliating admission of ignorance that ultimately led to his resignation. Now Incurious George's charge sheet can include the mistake of agreeing to be grilled by the Today programme. Less honest, more wily public figures than he have dreaded that ordeal, with an increasing number over the years refusing to grant interviews, and thus living to work another day.

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The trenchant and career-altering interview is such a mainstay of the media, whether in print or on air, that it's a surprise to learn how relatively recent it is. The first ever conducted was with the leader of the Mormon Church, Brigham Young, who was questioned by the New York Tribune in 1859. Three decades later, having seen the results of such interrogations, Rudyard Kipling fulminated against two reporters who had tried to corner him. "Why do I refuse to be interviewed?" he fumed, "Because it is immoral! It is a crime, just as much a crime as an offence against my person, as an assault, and just as much merits punishment. It is cowardly and vile. No respectable man would ask it, much less give it."

Since it began in America, it's perhaps appropriate that it was there that the form was elevated into an art. David Frost became the high priest of the modern age, not only for eliciting Nixon's admission to misdemeanours long after Watergate, but for conducting the first "trial by television". The victim of that extraordinarily heated encounter on The Frost Programme in 1967 was a fraudulent businessman, Emil Savundra. In a still deferential age, it was electrifying.

Editors quickly realised that the best interviews were those where the subject revealed something they'd told no-one before. Good journalists make such confessions appear inevitable, as if they'd have been offered up to anyone who happened to be passing, but no-one should underestimate the skills required to coax truth and secrets out of the reticent or the evasive. It requires the stealth of a big-game hunter, the ear of a therapist, and an eye for clues that Inspector Maigret would envy.

As a journalist who can barely bring myself to ask if a person is married or single for fear of being intrusive, I admire the nerve and courage it takes to probe further than seems polite, to risk turning a pleasant chat into a fraught encounter more like a duel than a duet. I was once asked by my editor to confirm rumours that a novelist had been a prostitute when she was younger. The chill that followed this inquiry still makes me shiver. Not surprisingly, the conversation ended at that point. What distinguishes the finest interviewers, however, is an utter lack of embarrassment. They refuse to be cowed by a put-down, or the threat of someone walking out and leaving their tape, or notebook, or recording studio empty.

It's become fashionable of late to bemoan the terrier tactics of inquisitors such as Humphrys and his peers, but those who criticise intrusive or aggressive questioners should perhaps be less squeamish. In the many interviews he gave over the years, Jimmy Savile dropped broad and frequent hints about his proclivities, and yet not one journalist pursued this line of questioning. As a result of their reticence, self-consciousness, or awe, he got off scot free. It seems to me that ruthlessly rigorous interviewing is not just an honourable trade, but a vital public service.