Insp Steve Evans said the sudden increase of smokers lighting up outside pubs and restaurants since the ban on July 1 last year has "provoked" trouble in the city centre.

He warned innocent smokers could fall prey to yobs intent on causing trouble by picking fights in the street.

And today, Lancaster police chief, Chief Supt Tim Jacques, said the ban has meant more people are staying at home to drink, sparking more violence in homes and neighbourhoods in the city.

Insp Evans told the Evening Post: "Our figures for violent crime in the city centre are roughly the same, but the focus is shifting on to the streets rather than in pubs.

"The smoking ban has put more people on the streets which can provoke trouble.

"It stands to reason. If there are 20 people stood outside in the street, someone walking the streets looking for trouble has more people to encounter and a bigger choice."

He added: "We are not saying smokers are responsible for violent behaviour - but those people stood outside having cigarettes would normally have been in pubs and not encountered the troublemaker."

This latest revelation comes two weeks after the Evening Post revealed how Church Street in Preston is the most dangerous street in Lancashire with more recorded violent crime than anywhere else in the county.

There were between 515 violent incidents in the city centre out of the 1,132 reported in Central Division between July and December 2007 compared to 488 from the 1,109 total for Central Division in the same period in 2006.

Ronnie Fitzpatrick, landlord of the Dog and Partridge, Friargate, Preston, said: "I think there is less tension in pubs because there is more room - the smokers are outside so not as many people bump into each other, which was often a source for trouble."

Insp John Ainsworth, of Lea Police, said: "People are staying at home more since the smoking ban. Traditionally people would go to the pub, get a takeaway on the way home and it was more relaxed."