Officers visited more than 80 pubs, bars and clubs in the city at the weekend, as part of Operation Badge.

It follows the introduction of new rules for bouncers by the Security Industry Association (SIA).

Door staff have to be professionally trained, qualified and security-checked to be employed in the role.

Insp Mike Cox said: "They are often dealing with people who are vulnerable or become violent due to drink and for this reason it is essential that they are security-checked and properly trained.

"All of the door staff who were issued with warning notices now have three months to get licensed, after which time we will carry out the same checks.

"Ultimately, door staff who are continuing to work without having applied, as well as those employing them, are committing an offence. If they haven't co-operated, then they risk having their premises closed down."

Staff must prove they are registered by wearing a badge.