London: Margaret Thatcher famously opposed the sale of the Royal Mail, insisting that she was “not prepared to have the Queen’s head privatised”.

So it is something of an irony that less than a year after the coalition government controversially sold off the venerable institution, the Royal Mail has decided to put Baroness Thatcher’s head-on a stamp for the first time. Thatcher is one of eight British prime ministers to feature on a set of stamps produced to mark the 200th anniversary of the office.

Though some of the leaders have appeared before (notably Winston Churchill, who has twice been honoured with his own set) this will be the first time a whole series of stamps has been dedicated to prime ministers.

The Thatcher stamp shows the “iron lady” in relaxed mode in a pale blue outfit gazing out towards the viewer on a first-class stamp. Other 20th century PMs whose faces appear on the first class stamps include Churchill, splendid in spotted bow tie, and providing political balance the Labour leaders Clement Attlee and a pipe-smoking Harold Wilson.

On the 97p stamps (for small items of airmail to Europe) are portraits of leaders from the 18th and 19th centuries: William Pitt the Younger, Charles Grey, Robert Peel and William Gladstone.

Andrew Hammond, a spokesman for Royal Mail, said: “As the UK is one of the oldest parliamentary democracies in the world, it is fitting that we mark eight individuals who have held the role over the centuries.”

Paul Lay, the editor of History Today magazine, said the selection was “intriguing”. “Some like Winston Churchill and William Gladstone need little introduction. Yet figures such as Charles Grey, though little known today, played crucial roles in some of British history’s most important events, including the great reform act of 1832, which set the country on the path to mass democracy, and the abolition of slavery.”

He argued it was right, too, that Thatcher was honoured. “Margaret Thatcher and Harold Wilson were major figures in important times and, whatever one’s political views, deserve their place in the selection.”

Thatcher, who privatised British Gas, British Airways, British Telecom and dozens of other state-owned institutions in the 1980s, refused to countenance a sale of Royal Mail.

The postal workers union CWU, which strongly opposed privatisation of the Royal Mail, politely declined to comment on whether its members would be happy delivering letters adorned by an image of Thatcher.

Choosing who appears on stamps is a painstaking process. For almost 50 years, Royal Mail’s special stamp programme has commemorated and celebrated events and anniversaries pertinent to UK heritage and life.

It receives many hundreds of requests for subjects for its stamps every year from the public, collectors and organisations. In addition it tries to commemorate any major anniversaries and events.

Royal Mail says it collates all the subjects and then carries out careful and extensive research to arrive at the final list of stamp subjects. The Queen approves all UK stamp designs before they are printed. The prime ministerial stamps will be available from 14 October. They can be bought individually or as a set in a presentation pack.