MPs have been accused of flouting the smoking ban - and even sneaking cigarettes in the Commons toilets.
Are MPs breaking their own smoking ban?
Although it is not illegal to smoke in the Palace of Westminster, both Houses decided to ban it from Sunday - the same time as the rest of England.
But Labour's Betty Williams told MPs the ban was "already being abused" and offered to show Commons leader Harriet Harman where people were smoking.
MPs joined in with cries of "division toilets" and "toilets".
Ms Harman, who was answering her first business questions since taking over as Commons leader under new Prime Minister Gordon Brown, said the issue should be raised with the Serjeant at Arms.
But she said she had been pleased to see "smoke enforcement officers in high visibility jackets" on her way into the Commons, which showed the ban was in operation elsewhere.
Mrs Williams said she had been contacted by the Serjeant at Arms after raising the issue in the Commons and he had agreed to put up more "no smoking" signs.
She said she had seen "three incidents" of people smoking in areas where they should not since the ban had been introduced.
"I don't see why I should have to go out through a door and walk into a cloud of smoke when there are four designated smoking areas," she told the BBC News website.
But the Conwy MP, who has been pushing for a ban on smoking in the Palace of Westminster for more than 10 years, said it was a "weakness" of the Parliamentary smoking ban that it was not backed up by fines or other sanctions.
The Commons authorities declined to comment on what penalties MPs and peers might face if they were caught smoking.
It has been suggested they could be reported to their party Whips, who are responsible for maintaining discipline.