But progress in the law often arrives late. Criminal barristers can be approaching 50 before they reach the top of their premier league. In court, age and treachery still triumph over youth and ability. The leading practitioner Nick Purnell, QC, 62, explains: “There’s simply no substitute for experience.”

His point is underlined by two big hitters: John Kelsey-Fry, QC, at the half-century and David Perry, who is 49: One admirer of “Kelsey”, as he is known, comments: “He has become an outstanding advocate in the past five years — up there with the best of them.”

A former senior Treasury counsel, Kelsey reveals that he learnt his craft “prosecuting pickpockets and prostitutes”. More recently, his jury skills have prevailed in the libel courts on behalf of Roman Polanski.

Then there is David Perry, of whom Monty Raphael, the doyen of criminal solicitors, says: “He is wonderful — very focused, not pompous, not arrogant. I was impressed with him as a young junior. Now he has really come into his own.” After Perry’s successful prosecution of Abu Hamza, a leading silk added: “David’s an excellent courtroom operator, hard working with a really good intellect.”

Set against Kelsey-Fry, Perry and other rising criminal talent at or under 50 — such as Aftab Jafferjee, Jonathan Laidlaw, Nicholas Hilliard, John Cooper and David Martin-Sperry — one barrister steals the superlatives. “She is outstandingly clever,” says her former pupil master, Stephen Batten, QC. “The brightest of them all,” confirms Ed Lawson, QC. “She has a beautiful mind,” adds Alex Cameron, QC.

The object of their admiration: Clare Montgomery, QC. At 48, she has been at the top for several years. “There is co-ordination, speed and obviously mental skill, which is my strength. There are so many nuances; no matter how good you are, you carry on learning.” This is how Montgomery describes her Millfield fencing career. Competing as a national junior, she “desperately wanted to win”.

Fencing matches provided useful training for the cut and thrust of the courtroom, although she admits to “still being nervous up to the point when I get on my feet”. After being labelled “a useless pupil” in civil chambers, she switched to crime and never looked back. “I find the law terribly dull,” she says, “unless it has a human content.”

Montgomery shone as a junior in big fraud trials. “Guinness began a new process of trying crime,” she says. “Maxwell was its litmus test. There was huge scope for lawyers to test the strengths and weaknesses of the system. The Serious Fraud Office had a starry-eyed notion that it was going to prosecute massive fraud cases. It now realises that criminal cases are best kept simple and straightforward.

“I’ve never had a big prosecution practice. I find prosecuting more of a strain because your obligations are more onerous.”

She is now advising the Crown Prosecution Service on what charges, if any, should be brought against the police officers involved in the case of Jean Charles de Menezes, shot dead last July in Stockwell Tube station.

It’s the latest in a long, newsworthy list. There was General Pinochet in his Lords extradition hearing. “A fascinating legal conundrum,” she says. “I look back with a mixture of loathing and distress — it was fantastically stressful, with strong emotions on all sides.” And the Sally Clark appeal against the murder conviction of her two baby boys. “Reading the papers, I was genuinely astonished. It was an obvious winner. I couldn’t understand how it had gone so wrong, how this woman was in prison.”

Montgomery claims that “there are only five cases in my career where my input may have made a difference to the outcome. Normally, you get an extravagant amount of praise relative to your effect on the result.”

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