Betty Boothroyd, the retiring speaker of the House of Commons, has rejected a plea from 85 MPs to change the election rules that will decide her successor.

The MPs had called on Boothroyd to remain in post for a short period to oversee the introduction of a system of democratic elections for the Commons chair.

She rejected the call to stay on, saying the rules used to elect her had been satisfactory and "provided they are understood and exercised properly, I see no reason why they shouldn't do so again on October 23".

Tony Benn last week wrote to the House authorities calling for a change in the Commons standing orders. He said that the current system, traditionally used after a favoured candidate had emerged through the "usual channels", is not practical when dealing with the unprecedented number of candidates who have put themselves forward to become speaker. He said a secret ballot followed by a run-off between the two top-polling candidates was the best solution. "With perhaps 10 candidates in the field, this is the only practicable way of dealing with the matter," he said.

In the race to succeed Boothroyd Labour MP Michael Martin remains the favourite. However, Margaret Beckett, leader of the Commons, and Ann Taylor, Labour chief whip, are understood to believe it would be better for a Conservative to have the chair to avoid the appearance of Labour having too much power. On the Tory benches the race is narrowing with Sir George Young and Sir Alan Haselhurst seen as the favoured candidates.