The ministers are not named in the book and other claims in the book about the agency's alleged spying in Canada have been denied.
The technician, Michael Frost - who was fired in 1990 for drunkenness, but now says he has beaten his alcohol problem - said the request came from the Government Communications Headquarters (GCHQ) apparently because the Canadian agency had the technical capacity and was less likely to be discovered than if the GCHQ had attempted the taps and monitoring itself.
Mr Frost did not do the monitoring himself, but he claims that a close friend in the agency visited London in February 1983 with a Microtel briefcase receiver and established himself in Macdonald House, part of the Canadian High Commission. The tapes of the intercepts were turned over to the GCHQ in Cheltenham, according to the book.
Mr Frost's co-author, Michel Gratton, an Ottawa journalist who worked briefly as press secretary to the former prime minister Brian Mulroney in the 1980s, speculates the Canadians were asked to do the monitoring so that GCHQ could distance itself from such activities should they become public.
Mr Frost claimed a GCHQ officer provided the frequencies the Canadians were to monitor and that the request came through top secret channels. Mr Frost quotes his friend, Frank Bowman, as saying, 'It seems as if Margaret Thatcher thinks two of the ministers in her cabinet are not 'on side' . . .
She wants to find out if they are.'
Mr Frost asked Mr Bowman when he returned from London what he had learned.
'It was interesting,' he replied. ' I don't know if Mrs Thatcher got what she was looking for. But to be honest, Mike, I might as well have been copying Hindustani because I can't understand these English accents anyway.'