A 51-year-old man was charged with racially aggravated harassment after police went under cover as restaurant diners to weed out customers hurling racist abuse at, or mimicking, staff.

Operation Napkin, begun in Gloucester last month to crack down on diners expressing unsavoury opinions in Indian and Chinese restaurants, used pairs of plainclothes officers eating out on Friday and Saturday nights.

"We feel the scheme has been a success already and made drunken people think it is not okay to racially abuse staff. Officers are not there to eavesdrop but to deal with overt racist behaviour," said Dean Walker, chief inspector in the Gloucestershire police, who denied the lack of more arrests so far meant racist incidents were not occurring.

Police are planning two operations a month, using surveillance at weekends from 11pm onwards to coincide with pub closing times.