Out of the 23 premises that were tested in the city centre, 16 admitted two girls aged 15 and 16, who were accompanied by plain clothed officers.

Insp Paul Winter said the results were "very disappointing".

He said licensees faced having their businesses closed if they continued and underage drinkers would be fined �50.

Insp Winter said: "The results from this operation are very disappointing and show yet again that people under 18 are gaining access to pubs and clubs, and being served alcohol.

"Despite the hard work already put in across the city, the processes are still going wrong somewhere.

"The premises that failed need to put in extra measures to ensure they improve immediately as this is completely unacceptable."