MPs should be given the final say over the date of a general election, says Labour deputy leader Harriet Harman.
Harriet Harman has called for an end to spin
Gordon Brown has faced calls for a fixed term Parliament after saying he considered calling an autumn election.
Ms Harman said she told Mr Brown he should seek MPs' approval before asking the Queen to dissolve Parliament - if he decided to go to the country.
It comes as poll for BBC Two's Newsnight suggests most voters think Mr Brown spins as much as Tony Blair.
Most voters say he has failed to live up to his promise to deliver an era of spin-free politics, the survey for Newsnight's Big Fat politics website suggests.
Mr Brown has been under fire from the opposition since he ruled out a general election until 2009, saying he needed more time to set out his "vision".
Conservative leader David Cameron accused him of "dithering" and lacking courage at a stormy Prime Ministers' questions on Wednesday - while the Lib Dems have called for a fixed term Parliament.
Speaking on Question Time, Lib Dem President Simon Hughes called for an end to the Royal prerogative, allowing prime ministers to ask for the dissolution of Parliament, saying: "power should reside with the people not with one person".
Ms Harman said she could "see the attraction of fixed term Parliaments" but said there "had to be some flexibility" to allow for outside events such as the 2001 foot and mouth outbreak.
But she said the prime minister should not be able to ask the Queen to dissolve Parliament before the mandatory five year term, saying "Parliament should decide whether or not an election is called".
"It is not right. The idea that the prime minister can simply choose to swish up to Buckingham Palace and get the Queen to decide on a general election," she told BBC One's Question Time.
She said she had told Gordon Brown that if he decided to go to the country, he should explain his decision to MPs.
"I did actually say if there was going to be a general election that he ought to come to Parliament and explain why there should be - if there was going to be one called."
Giving MPs the final say on dissolving Parliament is one of the issues being investigated by the select committee on the modernisation of Parliament.
It is also included in the government's green paper, The Governance of Britain, published in July, shortly after Mr Brown became prime minister, although Labour sources have stressed it is not guaranteed to become law.
Ms Harman also came under fire on Question Time over Mr Brown's pledge to end spin.
"I do think we did get into some bad habits and I think it's important that ministers when they are making announcements make them to Parliament, not through leaks and briefings to the newspapers. I think that's very important indeed," said Ms Harman.
She defended Mr Brown over his decision to announce troop cuts on a trip to Basra, apparently breaking his promise to make such statements in Parliament.
She said ministers should not leak announcements to the media before telling MPs - but Mr Brown's trip to Basra was made while Parliament was in recess.
"When the House is not sitting, the prime minister should not be in a position where he can not go on a visit, he can not actually make an announcement," she said.
The Newsnight/ICM poll suggests 61% of people believe the level of spin is the same as that under the previous prime minister, with a further 15% believing Mr Brown's government is more likely to spin.
The poll - conducted after this week's pre-Budget report - also suggests a clear majority believe the Labour Party has stolen Conservative policies on tax.
ICM interviewed a random sample 1,010 adults aged over 18 by telephone, between 10 and 11 October, 2007.