Smoking is outlawed in business premises and some company vehicles but enforcement officers say firms failing to put no smoking signs up will be prosecuted.

Many companies have failed to realise that a £200 fine could be imposed for failing to display signs in their premises.

Corby health improvement development officer Ted Greaves said: "When it comes to handing out fines it's unlikely to be to people smoking. Where companies are going to find themselves in trouble is with the signs they are required by law to display. Signs have to have the correct wording, it can't just be a simple circular No Smoking sign any more."

Company vehicles are also required to have no smoking signs if the car is, or could be used by more than one person. So, if an employee might allow a colleague to drive his company car, or if he may at some point give a lift to a colleague or client, smoking is banned in the car at all times and a sign must be displayed.

"The other thing that many employees don't realise is that it is the driver who will receive the conviction, not the company. At first we are giving out warnings, but after two warnings there will be a fine and it will be the individual who is convicted," said Mr Greaves.

Many companies say the new laws were well publicised in the weeks and months leading up to the new laws.

Director of A&R Print Solutions in Wellingborough Nigel Ogden said: "We received packs containing information and posters, so we knew exactly what we were required to do by law. Our vehicles and premises have proper signs displayed. We also got a pack at the cricket club I go to, so it seems like there was plenty of information out there."

Where there is likely to be most confusion is over the term "enclosed or substantially enclosed space".

A covered market stall with three sides, for instance, will be required to display no smoking signs. And hiring a marquee for a corporate function or private party could also leave those doing the hiring open to legal action.

Anthony Stobbart, key accounts director of The Marquee Company in Crick, said: "We now advise people that if the marquee has more than two sides, then it has to be smoke free.

"That only applies if people are being paid to be there, like catering staff or entertainers. If someone has a private party and doesn't bring in outside help, they are OK.

"There are structures that only have two sides, but if you want any more than that, then you are bound by the new laws.

"We will put up signs if our clients want us to, but once the marquee is hired out, it is the responsibility of the person hiring it to make sure the law isn't broken."