'Thank God my father is not alive to see this'

When Sir Mark Thatcher pleads guilty to involvement in a coup plot against an African leader today, it could well be the final act of a story where privilege has ultimately led to failure and shame.

When Sir Mark Thatcher pleads guilty to involvement in a coup plot against an African leader today, it could well be the final act of a story where privilege has ultimately led to failure and shame.

It was said to be his mother, Baroness Thatcher's, dearest wish that her son should inherit the baronetcy from his father, Sir Denis. At the time, observers said it was compensation for the loneliness Mark felt as a child, growing up while her career took precedence. His constant refrain during telephone calls back to London in recent weeks is said to be: "Thank God my father is not alive to see this."

He was delivered by caesarean section, along with his twin, Carol, and growing up a Thatcher was not easy. His father was already a millionaire businessman, his mother on course to be Prime Minister - expectations were high from the start.

But Mark failed to thrive academically. At Harrow, he picked up the nickname "thickie", passing just three O-levels. Accountancy proved equally taxing - he failed his professional exams three times. He flirted with the City, travelled to Hong Kong and served as a jewellery salesman. But Mark harboured an image of himself as an action man, a playboy even. His first foray into motorsport with Mark Thatcher Racing ended in cash-flow problems. And his obsession with fast cars and adventure led him to becoming a laughing stock with the British public, and reducing the Iron Lady to public tears.

Three years into his her premiership, he took part in the 1982 Paris-Dakar rally. Unprepared, he was soon lost in the Sahara desert. His father flew out to help with the search, which drew on the military support of friendly governments in the region. A large press pack was in tow.

When he eventually made contact, the young Thatcher refused to admit it was his fault. He declined to accept he had been lost at all. Adding to the growing impression of arrogance, he greeted the newsmen with the Bruce Forsyth catchphrase "nice to see you, to see you nice". Refusing to shake hands for the photographers with his by-now humiliated father, his reputation never recovered.

Warning bells over his conduct had rung before the desert fiasco. He had arrived in Oman at the same time as his mother, who was on official business. He was operating an "international consultancy firm", Monteagle Marketing, acting as a facilitator, introducing people he thought could do business together. He came to embody the type of businessman that his mother's critics said flourished during her years in power.

A devout believer in the free market, he thought he had the right to do business wherever and with whomever he chose. His single biggest asset, however, continued to be his name and his opponents say it was this he used to short-cut the usual route of expertise and experience through which conventional fortunes are built.

In 1984, it emerged that, while in Oman at the same time as his mother, he helped secure a multi-million pound deal for Cementation as part of a project to build a university. Two years later, by now married to the Texan millionairess Diane Burgdorf and living in the United States, he returned to the Middle East.

This time it was alleged he played a role in brokering a deal between British Aerospace and the Saudi government, earning him a commission of around £12m. The sale, part of the notorious al-Yamamah arms deal signed by Lady Thatcher, is said to have formed the bedrock of his £60m fortune. Luckily for his mother, it was not until she had made her final, tearful exit from Downing Street that the story broke.

The "Mark problem" was an enduring feature of her reign. He was disliked not just by the media but by senior government officials and even Tory ministers. When he asked Sir Bernard Ingham, Lady Thatcher's former press secretary, how he could help his mother win the 1987 general election, Mr Ingham replied: "Leave the country." Wherever he went, trouble seemed to follow - it seems as if it might have caught up with him now.