Margaret Thatcher died a multi-millionaire, having made the same discovery as other prime ministers before and since that she could make more money in semi-retirement than when she was in office.
Her wealth was augmented by her marriage to Denis Thatcher, who was a successful businessman before they met. He sold his business to Castrol in 1964, for £530,000 (equivalent to substantially more than £8m in today's money), though his personal share of the proceedings was only £10,000 or about £158,000 in today's money. But he continued for several years as a director of Castrol, and then of Burmah Oil, after it bought the company.
As long ago as 1991, she was reported to be commanding a fee of $50,000 (£33,000) per lecture in the US. One US newspaper speculated in May 1991 that she would make $1m (£650,000) from just one month on the lecture circuit. Rupert Murdoch also paid her an advance of at least £200,000, through his publishing firm HarperCollins, for her memoirs, published in 1993.
The initial volume, The Downing Street Years, went on sale on a Sunday in October 1993, and by Wednesday was reported to have sold 300,000 copies. The total sales are not known, because it was released before accurate sales figures were compiled, but it is assumed that it brought her millions in royalties.
Her estate is likely to make a substantial amount more because the two volumes of her memoirs covering 1,344 pages, have been distilled into a single 832 page volume, which is being rushed out by HarperCollins and can be expected to shoot straight into the non-fiction sales charts.
She also owned the house in Chester Square, Belgravia, which has repeatedly topped the list as the country's most expensive street. The average house price in 2010 was £6.6 million, and while no Chester Square property has been put up for sale in the past year, during the 2009 slump in property prices there were 10 on the market for prices ranging from £4,950,000 to £14,750,000.
The estate is expected to go to her son, Sir Mark, daughter Carol, and to Mark's children, Michael and Amanda, from his first wife, American-born Diane Burgdorf, whom he divorced in 2005.