Mrs Thatcher gave us several lectures on bringing up children, so I was intrigued to see what kind of a job she made of bringing up her dearly beloved son for whom nothing (including the SAS being sent out to search for him when he got himself lost) was too much trouble. This from Wikipedia
Having taken various short-term jobs he [Mark] moved to Hong Kong, where he built up a network of business connections, particularly in the Middle East and in motor racing. In 1977 he set up Mark Thatcher Racing which ran into financial difficulties.
During the mid- to late 1980s concerns were frequently expressed in relation to his business affairs. In 1984 his mother faced questions in the House of Commons in relation to his involvement in representing a British company Cementation, a subsidiary of Trafalgar House to build a university in Oman at a time when the prime minister was urging Omanis to buy British.
He has denied claims made that in 1985 he received millions of pounds in commission in relation to the £45 billion Al-Yamamah arms deal, a controversial arms sale by BAE to Saudi Arabia which was possibly the largest arms sale ever; he has not disputed that a house in Belgravia , London was purchased for him for £1 million in 1987 by an offshore company controlled by Wafic Said, a middleman in the deal. In 1986 his mother faced questions in the House of Commons again over her son's relationship with the Sultan of Brunei.
The government's PR advisers suggested that it would be best if he left the country. Alan Clark mentions the 'Mark problem' in his published diaries. He moved to Texas, where he worked for David Wickins of Lotus Cars and British Car Auctions and met his first wife in 1984. In the USA he started Monteagle Marketing which was a profitable company selling whisky and clothing. During this period he spent time in Switzerland as a tax exile until he was forced to leave when the Swiss authorities started to question his residency qualifications. He helped arrange the valuable contract for his mother's Downing Street memoirs in the 1990s. A security alarm business he ran in the USA failed and in 1996 he was prosecuted for tax evasion, at which point he moved to Constantia, South Africa with his wife and their two children.
In 1998 South African authorities investigated a company owned by Thatcher for allegedly running loan shark operations. According to the Star of Johannesburg', the company had offered unofficial small loans to hundreds of police officers, military personnel and civil servants and then pursued them with debt collectors. He claimed that officers had defrauded him and charges were dropped.It was also suggested that he had profited from contracts to supply aviation fuel in various African countries. In 2004 he was arrested in South Africa in connection with the 2004 Equatorial Guinea coup d'état attempt(see below), and pleaded guilty in January 2005 to breaking anti-mercenary legislation. At this time the Sunday Times suggested that he had personal assets of £60 million, most of which was in offshore accounts. (Mr Osborne may be able to mention this to him at the wake.)
Following his guilty plea he left South Africa and lived in Monaco for one year on a temporary residency permit; this was not renewed as Sir Mark was said to be on a list of 'undesirables' who would not be allowed further residency and he was required to leave by mid-2006. His wife and children moved back to the USA, but he was refused a entry visa due to his conviction in South Africa. He was refused residency in Switzerland and settled in Gibraltar where he married his second wife in 2008. In 2013 he was reported to spend most of his time in Marbella. He was in Barbados when he received news of his mother's death.