“It really looks like it was her private letter paper,” antiquarian Katja Burmester told The Local.
She said she found it in a copy of the book “The Downing Street Years” which had been in a box of books she had bought and was sorting through in her shop in Wismar near Rostock.
The book was not an official published copy, but an early edition without an ISBN number, probably one of a few given to Thatcher to give away, she said.
The letter carries a crest of Thatcher's address at the House of Lords – where she had a seat after being made baroness. Now 86, she was British Prime Minister from 1979 until 1990.
“To my husband and family, without whose love and encouragement I should never have become Prime Minister,” the hand-written but unsigned letter reads.
“And to all those who worked at 10 Downing Street and Chequers in whatever capacity whose unfailing support was crucial in those challenging years.”
“People bring me boxes of all sorts of books when they move, or when someone dies," Burmester said. "I buy them, and then sort through to find the interesting ones which I can sell.
“I don't even know how long I've had this for. But it is a bit special, I hope to sell it now, to the highest bidder.”