Just how rich is Margaret Thatcher? When she was ousted as prime minister less than five years ago, she had no significant wealth. Today, estimates are that she has accumulated at least pounds 9.5m and has entered the league table of the richest women in Britain.

Comprehensive figures, in the way of these things, are hard to come by. Some indications have entered the public domain. Her memoirs, the second part of which begin newspaper serialisation tomorrow, have netted her more than pounds 3.2m. Her appointment as a non-executive director of the tobacco firm Philip Morris reportedly brings an annual pounds 550,000. And then there are her repeated forays on to the international speaking circuit, where she can command pounds 50,000 an hour; one engagement in New York earned her pounds 150,000 for a single speech.

Her first trip to Japan after leaving office, which was organised by Lord Archer, brought in around pounds 2m, according to informed sources. She has kept up a relentless pace of speeches to foreign business people since. This year, so far, she has visited Spain, the United States, Singapore, Italy, China, Hong Kong and Bahrain, and she is in Japan again now.

Piecing together a total income is made doubly difficult because Lady Thatcher keeps part of the money for herself and donates part to the Margaret Thatcher Foundation, which was set up to promote her ideas around the world, particularly in Eastern Europe. Its aim was to raise pounds 10m from Thatcher admirers across the globe, but the response has been comparatively disappointing - thanks to the recession, say her friends - so Lady Thatcher has tried to raise money herself from world tours.

The foundation is a private company, which also has a charitable trust. Under regulations introduced by her government to cut red tape for small firms and preserve their competitive secrets, the foundation is not required to make full disclosure of its accounts. The latest set of abbreviated accounts filed with Companies House reveals nothing about the income and expenditure of the foundation, only that it ended the year 1993 with pounds 466,731 in cash and pounds 452,510 in assets.

Even less is known about the charitable fund. "It's a private trust; we can't disclose any details," says Vicky Pulman of the Charities Aid Foundation, which administers the fund. So who scrutinises it to ensure that it spends its money on the purposes set out in its deed of trust? "The Inland Revenue, the Charity Commissioners and the CAF trustees." But the accounts are not available to members of the public, even those who may have made donations. The trust is currently reported to contain around pounds 1m.

Accounts filed by the foundation's Washington office - which names Mark Thatcher as president of its US branch - are a little more revealing. Last year, Lady Thatcher's admirers gave it pounds 800,000. Of this, only pounds 79,000 (less than 10 per cent) was donated to projects in Eastern Europe. But pounds 158,000 was spent on fund-raising and pounds 57,700 on administration. At the end of 1993, there were net assets of pounds 793,855, with pounds 511,062 invested in blue-chip stocks.

Mark Worthington of the Thatcher Foundation estimates that to date it has raised around pounds 6m. Other informed estimates suggest that the former prime minister herself may have made as much as pounds 30m. The lady may be for earning, but she's not for telling.