Labour prime minister James Callaghan plotted to sideline Tory leader Margaret Thatcher during celebrations to mark the 50th anniversary of women gaining the vote, according to papers made public today.

As the first woman to lead a major party, Thatcher was by far the most prominent female politician in the country. But files released by the National Archives under the 30-year rule show that Callaghan was furious when he discovered she was to speak alongside him at the opening of an exhibition on Suffragettes at Parliament.

Lady Birk, junior environment minister in charge of the commemorations, was summoned to No 10.

She tried to placate the PM, telling him: “If you appear together, the contrast between your reassuring authority and her shrillness would be striking.”

Mr Callaghan got his revenge by ensuring Mrs Thatcher was excluded from the royal box at a gala performance at the London Palladium. His private secretary, Ken Stowe, advised him: “As I understand it, Princess Margaret’s attendance at the gala will require most of the royal box to be allocated to her and her suite and in all probability if you were to attend with Mrs Callaghan (and a political adviser) there would be no room for anybody else.

“I think, with a mixture of sweet reasonableness and low cunning, we should be able to fix it.”