The heir to an estimated £4 billion banking fortune accused of hiring detectives to hack into a computer belonging to his wife is incapable of reading a comic and cannot manage his bank account, a court heard today.

Tamara Mellon, boss of the Jimmy Choo shoe empire, giving evidence for the prosecution, told a jury how her former husband, Matthew, suffered from bi-polar disorder, could not properly look after himself and "missed planes like other people missed buses".

He is alleged to have hired private detectives to install a Trojan spy program to spy on her computer during an acrimonious divorce.

Ms Mellon, 37, who runs a fashion business valued at £180 million, which she founded with a £150,000 loan from her father, told Southwark Crown Court, South London, how she even worried about her husband, whom she met at Narcotics Anonymous in 1997, being alone with their daughter because he was so absent minded.

During cross-examination from Nicholas Purnell, QC, representing Mr Mellon, the full scale of the multi-millionaire’s problems were made public, including slurred speech, memory loss, insomnia and mood swings when he did not take his medication.

Ms Mellon agreed he was illogical and someone who “misses planes like other people miss buses”.

Mr Purnell said: “If he has a taxi coming for him he is likely to be in the shower or trying to get ready when it arrives.”

“What you are describing is mild,” said Ms Mellon.

“A day does not go by when Matthew does not lose his keys, mobile phone or wallet. I have been to the airport with him on several occasions when he does not have his passport.

“For a long time I didn’t want him to be alone with our daughter just because he is so absent minded. I wanted him to be supervised even though he is a fantastic with her.”

The couple still see each other every day when they are both in the UK as Mr Mellon picks up their daughter to take her to school. But Ms Mellon said she would have to ring him to make sure he remembered.

Ms Mellon sat in the dock wearing black £2,000 Jimmy Choo crocodile skin shoes with a 4in stiletto and carried a £2,000 cream, snakeskin Marin clutch bag; she wore a white top and cream cashmere Prada cardigan with an Yves Saint Laurent belt and Roland Mouret woolen pencil skirt. The small tattoo on her right ankle could not be seen.

The court heard how Mr Mellon was on the anti-depressant drug Lithium but was on too strong a dose.

She agreed with counsel on several points, including the fact that her former husband is unable to remember things said to him, only gets, at most, four hours sleep a night.

“He misses links in communication?” asked Mr Purnell. “Yes”, said Ms Mellon.

“He is not like other people?” “Yes, that is correct.”

“He can’t even read a comic let alone a legal document. There is no way he could do that,” she added.

She said that in the ten years she had known him he had never read a book. “Never, never, he could not focus, he could not get beyond the first page,” she said.

She agreed with a list of characterisations of Mr Mellon from his counsel, including that he was “very forgetful”, “not lazy, but incapable of analysis and needs to be told the bottom line”, has “no real business plan” and is “very sweet”.

Asked if he made notes to cope with his memory loss she said: “No, he would not be capable. He is too absent minded. He would lose the piece of paper if he wrote a note, that would be typical.”

Ms Mellon, whose father, Tommy Yeardye, transformed Vidal Sassoon into a worldwide brand, also agreed that although Mr Mellon believed he played a significant part in her business life he was more a companion that associate.

“Being married to Matthew was like having another child. Matthew cannot manage his bank accounts, can’t pay his bills. When we were married I had to take responsibility for managing the bank account and do the bills because he was totally incapable.

Mr Purnell: “He needs a nanny”

Ms Mellon: “Correct”.

Mr Purnell: “He needs a mother, wife, best friend.”

Ms Mellon: “That’s correct”.

Mr Mellon is alleged to have used Active Investigation Services (AIS) between July 2004 and February 2005. He is one of several British-based businessmen accused of using the detectives to snoop on their wives, through phone-tapping or computer hacking.

The court has heard that the couple, who married in a glittering ceremony at Blenheim Palace in 2000, separated in 2004 after Mrs Mellon began an affair with Oscar Humphries, son of the comic actor Barry Humphries.

Miranda Moore, QC, for the prosecution, said that Mr Mellon employed AIS's services to "snoop on his wife" during divorce proceedings because he wanted information he was not getting through the court process.

Ms Moore said that AIS paid an American hacker to install a Trojan spy program on her computer hidden in an e-mail that "purported to show what her husband was up to".

Mr Mellon, of Belgravia, denies conspiring to cause unauthorised modification of computer material.

The trial continues.

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