One of Britain’s top judges brandished a pair of black Calvin Klein briefs in court today to defend himself against a charge of flashing a young woman on a busy commuter train.

Sir Stephen Richards, a Court of Appeal judge, held up the designer briefs - more often associated with the footballer Fredrik Ljungberg than the judiciary - and explained that they were similar to the ones he usually wears. He told the court that it would have been difficult to expose his penis while wearing them as it usually required both hands.

Lord Justice Richards, 56, told the court he was “astounded” when he was arrested by police. He is accused of twice cornering a young woman on the commuter train to Waterloo and deliberately exposing himself to her.

The woman says that she saw the man on four separate rush-hour journeys from Raynes Park, southwest London and alleges that he exposed himself twice. She said she felt “shock and embarrassment” at being flashed on a busy train.

David Fisher QC, Sir Stephen's lawyer, asked him: “In order to remove your penis when you’re wearing your Calvin Klein briefs is it necessary to use one or two hands?”

The judge replied: “If I had a pee, I would use two hands. It is the natural way of doing it.”

Sir Stephen was in court with his wife and two of his children, Matthew, 27 and Tom, 25. “I have no desire to engage in such behaviour whatsoever. I am a happily married, family man and I cannot perceive deriving any form of gratification to exposing my penis,” he said.

The judge said he could not remember the precise details of his commutes on October 16 and October 24 last year, but he strenuously denied the accusations.

“I am a judge I know whose responsibility is not just as an ordinary member of society, but also in my judicial capacity it is conduct I would not engage in,” he said.

The woman said she thought Sir Stephen, who was wearing a raincoat, was displaying his genitals accidentally on the first occasion because he was “presentable and looked like a very kind man”.

“Because I was embarrassed and nothing like this had happened to me before, I assumed this was an accident. I did not want to draw attention to the situation, to me or to the gentleman, so I carried on reading my paper,” she told the court.

“Sometimes the gentleman would adjust himself slightly, sometimes his genitals would be exposed and sometimes not as much.”

A week later, on October 24, the witness said she saw Sir Stephen once again. This time she could see that his flies were undone from below her newspaper, she took out her mobile phone in an attempt to unnerve the man, who then moved away.

She later took two photographs of him, as he left Waterloo station, and reported his behaviour to the police.

Sir Stephen was called to the bar in 1975 before rising through the ranks to become a High Court judge in 1997. He pleaded not guilty to two counts of “intentionally exposing his genitals intending that someone would see them and would be caused alarm or distressed”.

The judge admitted to owning a beige raincoat, but claimed: “It is a mistaken identity.”

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