England slammed the door on smoking in bars, workplaces and public buildings on Sunday in what campaigners hail as the biggest boost to public health since the creation of the National Health Service in 1948.
The chief medical officer Sir Liam Donaldson said there would be teething problems with the change, but he expected people to comply with the new law.
He told BBC TV: The other places that have introduced it, both overseas and also the other UK countries, have had very few problems.
England is a very big country so there are bound to be some teething problems with implementing it.
But on the whole, the majority of smokers and non-smokers wanted this change, so I expect people to comply with it very, very straightforwardly.
He said he expected a reduction of more than 1 percent in the number of smokers as a result of the ban.
Deborah Arnott, director of charity Action on Smoking and Health, welcomed the ban. She said: Smoking is the single most preventable cause of death.
Workers have a right to a safe environment and the harm done by tobacco smoke is now known to be significantly dangerous.
But artist David Hockney, who has been waging a campaign against the ban, called it a grotesque piece of social engineering imposed by a political and media elite.
The English ban means smoking in enclosed public places such as pubs will now be banned across the entire United Kingdom.
Wales and Northern Ireland outlawed public smoking in April following the lead of Scotland last year.
Ireland and other European countries have also banned smoking indoors, while some parts of Canada and a number of U.S. states have had strict controls on smoking for years.
The legislation is designed to protect people from the effects of second-hand smoke at work, which doctors estimate kills more than 600 people a year.
A quarter of adults smoke, with the level higher among those doing manual and routine jobs.
Individuals lighting up against the law face fines of up to 200 pounds while businesses can be charged up to 1,000 pounds for failing to display no smoking signs in affected areas which also include minicabs, company cars and churches.
Offshore oil rigs, hotel rooms and prison cells are among the few places where public smoking will continue to be permitted. People will also still be able to smoke at home.
Not everyone supports the new laws but most are resigned to them.
Richard Lilley, a 37-year old law firm printer relaxing with as cigarette and pint of beer in a pub in London's Fleet Street said he did not want to give up smoking because he enjoyed it.
I won't bother going to the pub, I will drink at home. I enjoy a beer with a cigarette, it's part of the culture.
Others will sit or stand outside, with many pubs installing rain awnings and patio heaters to accommodate smokers.
(Additional reporting by Simon Rabinovitch)