Ahead of her 1979 election win, former British Prime Minister Margaret Thatcher was on a protein-packed crash diet that included 28 eggs a week, according to newly released personal documents.

The diet to be followed for two weeks with an intention to shed 20 pounds (9kg), was outlined in a note found in a diary from that year.

"I think she was looking to get in trim for the cameras," says Chris Collins of the Margaret Thatcher Foundation (MTF), which has released thousands of papers covering the period between May and December 1979 to Cambridge University.

"She probably thought: The cameras are going to be on me the whole time - I'm going to lose some weight," said Collins.

"But she is not somebody who had a problem with weight at all. She is on the move the whole time - she burns energy."

The diet -- outlined in the yellowing note found inside her 1979 black leather pocket diary -- included a daily breakfast of grapefruit, one or two eggs, black coffee or clear tea.

"Two eggs were served in each of her weekday lunches, while steak, lamb chops and fish were the staple of most dinners," the Sky News reported.

The majority of items were ticked off - but small crosses appeared next to items including eggs and grapefruit on the Monday, it said.

The neatly folded piece of paper, which warned the diet should not be followed for more than two weeks, is headed up "The Mayo Clinic Diet".