There could be a free vote of MPs on having a complete ban on smoking in public places in England.
A partial ban would widen health inequalities, opponents say
Ministers told Labour MPs they were considering the idea after an amendment was tabled calling for the total ban.
Many backbenchers are angry that the Health Bill, as it stands, would allow smoking to continue in private clubs and pubs which do not serve food.
Health select committee chairman Kevin Barron said he was "quite optimistic" that a free vote would take place.
Mr Barron, who met Labour chief whip Hilary Armstrong on Tuesday, said a free vote would apply not just to backbenchers but to all Labour MPs, including ministers.
He added: "If carried, our amendment will greatly strengthen that part of the bill which aims to protect the public from the dangers of second hand smoke.
"Since 1997 this government has come a long way towards controlling the harmful effects of tobacco use and this is another milestone towards the improvement of public health."
The partial ban plan was put forward by the government after several days of argument within the Cabinet.
Health Secretary Patricia Hewitt, who was thought to back a total ban, has since said she expects all smoking in enclosed public spaces to be outlawed within a few years.
The cross-party amendment to the Health Bill will be considered in a couple of weeks when it returns for its report stage in the Commons.
Labour MP Andrew Mackinlay told BBC News 24: "If backbenchers get a free vote... there will be a total ban."
Last month, 64 Labour MPs signed a motion calling for a free vote.
Conservative MPs have also been promised one.
In a recent report, the Commons health select committee said a total ban was the "only effective means" of protecting public health.
A partial ban would "widen health inequalities" and "be disputed in the courts", the MPs added.
But Health Minister Caroline Flint said it represented "a huge step forward for public health".
Some Conservative and Lib Dem MPs are thought to oppose a total smoking ban for fear it could undermine civil liberties.
Tony Blair has promised to "listen to the debate with interest".
The partial ban being proposed is the one which was enclosed in the Labour manifesto at the 2005 general election.
The government has agreed to stop smoking in all pubs and clubs in Northern Ireland, and the Scottish Executive has ordered a ban.
The Health Bill gives the Welsh Assembly the right to decide for itself whether to implement a ban it has already twice approved in principle.