Lady Thatcher is said by members of her former staff at No 10 to hold an "Aladdin's cave" of material. One of the documents is an unpublicised journal kept during the Falklands war in 1982, which experts say would be likely to fetch an enormous sum at auction.
Chris Smith, the opposition National Heritage spokesman, is writing to John Major this week. He said he wanted to know "what papers, if any, Mrs Thatcher took when she left office and whether ones she may be working on are regarded as on loan or whether they are regarded as being hers".
Some fear that her son Mark will see a commercial opportunity in the future, and benefit as Mr Churchill may do from the sale of his grandfather's papers, purchased by the Government last week with £12.5m of National Lottery cash. Mr Smith said that rules "must be rapidly established" if Lady Thatcher, or any other ex-PM, had "spirited away" papers.
But a former close adviser said she would probably hang on to them, but added: "She wouldn't just give them up to the nation, it's not in her nature. She's certainly not averse to money and might well sell them, especially when she sees how much the Churchill papers got."
Yesterday it was revealed that Winston Churchill will not, after all, become a multi-millionaire as a result of the sale of the archive but, he will probably share the income generated by the capital sum. Theoretically, the trustees of the archive could decide he is ineligible even for that.
"People have been assuming that he will receive £12.5m," Peregrine Churchill, the former prime minister's 82-year-old nephew and a trustee, said yesterday. "But the trustees have 100 per cent discretion as to what they do."
How the deal was done, page 3