A total smoking ban is now the most likely outcome after Prime Minister Tony Blair hinted he would allow a free vote on the issue.
Speaking in The Observer, Blair said that chief medical officer Liam Donaldson was "absolutely right" to call for a total ban in place of the Government plan to exempt drink-only pubs and private clubs.
"I do not think there is any great point of principle," he said. "But simply what is the right thing to do."
He added that he considered smoking to be in a different category to core reforms such as education.
Although, officially denying there would be a free vote, it is expected the whips will go easy on those who choose to rebel.
The third reading of the bill is due to be heard by the end of the month when amendments will be debated.
Labour MP and chairman of the health select committee Kevin Barron, who blasted the current proposals as "unworkable", is expected to table an amendment calling for a total ban by the end of the week.
A total of 70 Labour MPs have signed an early day motion calling for a free vote, including All-Party Parliamentary Beer Group chairman John Grogan. A further 56 Labour MPs have signed a motion calling for a blanket ban to be introduced.
Grogan rates the odds of a free vote being granted as 50-50.
However, he warned that the probable outcome of a free vote would be a total ban. "The danger of a free vote is that it could end in the worst possible case of the food exemption being removed but clubs being kept in," he said.
"If there is a free vote, I think the trade associations have got to be quick off the mark to lobby for the inclusion of clubs."
Grogan added that there were now only three options left open - the Government's food-based ban, a total ban or the worst possible case scenario of clubs being left exempt. "I would now favour a total ban," he said.
The Tories will grant its members a free vote while the LibDems are known to favour a total ban.