Mrs Thatcher's apparent motto is revealed in National Archive files
"Never admit to anything unless you have to" was apparently a rule that former prime minister Margaret Thatcher liked to live by.
Documents from 1979 released by the National Archives show she used the rule to argue against publishing a book on the secret services.
Other files reveal her efforts to be seen as an equal to male world leaders.
They show that when Japan tried to give her female bodyguards - so-called "karate ladies" - she refused.
'Stick to it'
The newly-released records reveal how different politicians reacted to plans to publish an official history of Britain's intelligence services in World War II.
Prime Minister Jim Callaghan wrote to Mrs Thatcher, then in opposition, and Liberal Party leader David Steel telling them that "[the book] gives credit where credit is due" but does "not attempt to cover up the faults".
Mr Steel agreed to publication, but Mrs Thatcher expressed her disquiet, asking: "Do we really have to lay bare to those who could profit from it, not only what intelligence we had, but how we interpreted it?"
She went on: "I was taught a very good rule by two Masters at Law, both of whom are now judges: never admit anything unless you have to; and then only for specific reasons and within defined limits.
"It is a rule that has stood me in very good stead in many a complicated matter, and in the absence of further advice I should be inclined to stick to it now."
Mr Callaghan was also in favour of releasing documents marked with SIS, indicating that the Secret Intelligence Services - MI5 and MI6 - had been involved in their preparation.
But at the time, the policy of the British government was to deny the existence of the secret services - and Mrs Thatcher wanted to stick to that.
Mrs Thatcher wrote to Jim Callaghan expressing her "disquiet"
She said the publication of the documents would be "the thin end of a dangerous wedge".
In his reply, Mr Callaghan admitted it would "make it the more unrealistic to maintain the fiction that this organisation does not exist at present".
But he insisted: "This would be on the very clear understanding that avowal that the service exists should not result in giving way to any pressures to answer questions about it."
Another file released by the archives gives a glimpse at how the arrival of a female head of government opened up a new minefield in diplomatic etiquette.
Ahead of the Tokyo international summit in June 1979, a document from the government's Protocol and Conference Department revealed that Japanese authorities were planning to provide 20 "karate ladies" - specialist female bodyguards - to attend to her.
Mrs Thatcher was a lone female on the global political stage
But a letter from the Lord Privy Seal to the Foreign Office made clear Cabinet Secretary Sir John Hunt's view that "Mrs Thatcher will attend the summit as prime minister and not as a woman per se".
It continued: "The prime minister would like to be treated in exactly the same manner as the other visiting heads of delegation; it is not the degree of protection that is in question, but the particular means of carrying it out.
"If other delegation leaders, for example, are each being assigned 20 karate gentlemen, the prime minister would have no objection to this; but she does not wish to be singled out.
"She has not had in the past and does not have now any female Special Branch officers."