Almost 700,000 smokers would kick the habit within the first year of a total ban on smoking in public places being introduced, research suggests.

Campaigners hope the finding will increase pressure on MPs to back a total ban when they have a free vote on the issue next month.

The campaign groups Action on Smoking and Health (Ash) and Asthma UK predict that 689,000 smokers in England would give up during the first year of a total ban.

One in four of the population currently smokes regularly, rising to 39 per cent of all adults in "hot spots" such as Kingston upon Hull.

The Government had proposed to introduce a partial ban from summer 2007 that would only outlaw smoking in pubs and restaurants that serve food.

The chief medical officer, Professor Sir Liam Donaldson, considered resigning as he wanted a total ban and health campaigners were outraged that the law would exempt pubs in the poorest areas with the highest rates of smoking. The Prime Minister agreed earlier this month to let MPs have a free vote on the Bill, which could see them back amendments for a total ban.

Deborah Arnott, director of Ash, said: "We are now within sight of the most important advance for public health in many decades."

The research did not estimate how many people would quit if a partial ban was introduced, but the two charities say that the impact would be much reduced if some pubs and restaurants were excused.

It is known that more than 100,000 people in New York stopped smoking within the first year of the introduction of a partial ban on smoking in public places. Sales of cigarettes in Ireland fell by 16 per cent in the first six months of a smoking ban imposed in in 2004. The investment bank Morgan Stanley has predicted that cigarette consumption in England will fall by 5 per cent this year as a direct result of the ban.

The British Beer and Pub Association declined to comment on the study ahead of an announcement it is making today on the Bill.