The Bill to ban smoking in public places in England comes before the Commons today following days of wrangling among Cabinet ministers.
Smoking will be outlawed in restaurants, pubs and bars serving food - but private clubs and food-free bars will be exempt.
Health Secretary Patricia Hewitt faces an uncomfortable grilling by senior MPs over her U-turn on the proposed ban.
Exemptions for clubs and some pubs has provoked fury from health experts and anti-smoking groups.
Backbench Labour MPs and TUC boss Brendan Barber joined health experts in condemning the decision.
There were also suggestions that the mix-up showed Tony Blair was losing his authority as Prime Minister.
Ms Hewitt had been seeking tougher measures and had publicly described the proposals as "unworkable".
Critics blamed her predecessor Dr John Reid, now Defence Secretary, for forcing colleagues to abandon a more wide-ranging ban.
Dr Reid was adamant that private members should be allowed to decide whether or not smoking was allowed.
Ms Hewitt will have to defend the plans before the Commons Health Select Committee.
In a statement, she said membership clubs will be exempt from the ban and non-food pubs and bars will be "free to choose whether to allow smoking, or be smoke-free".
Smoking at the bar will be prohibited in all venues.
The Government will hold consultations on how to implement the policy - whether by introducing separate smoking rooms or areas to protect staff.
Scotland, Wales and Northern Ireland are already following the Irish Republic and New York in introducing total bans, Sky News reports.