Pubs with late licences are being urged to check their conditions to ensure they avoid prosecution over the smoking ban.
Warwickshire Police has written to licensees warning them to check if they have a licence condition banning people from being in an outside area after 11pm.
Under the Licensing Act, some pubs also have a condition preventing re-entry after 11pm. Pubs failing to adhere to these conditions would face prosecution or a licence review, Warwickshire Police has warned.
A letter sent to licensees said: "The police seriously value the conditions will continue to do so when the smoking ban takes effect.
"You would be in breach of your licence if you allow your customers outside with these restrictions in place and ultimately you may be prosecuted through the courts and/or a review of your licence."
The letter also calls for pubs without conditions to look at how to deal with potential anti-social behaviour caused by the ban.
But Philip Stone, licensee of the Peeping Tom, Coventry, which has a licence until 12.30pm, is worried about the implications. "I foresee more than a few unpleasant exchanges with customers when I say thank you for going outside to smoke, but sorry you can't because the garden is closed. I am concerned as to how many other licensees have neglected to take this into consideration."
Sandra Barfoot, licensee at the Cape of Good Hope, in Warwick, which has a midnight licence on Fridays and Saturdays said: "We're in quiet area and people would have to go away from the pub to have a cigarette outside of our supervision, which could cause problems."
Tony Payne, chief executive of the Federation of Licensed Victuallers' Associations, urged publicans to check the wording on their licences. "Smoking is not a licensable activity, whereas drinking is, so you cannot stop people going outside," he said.