An Oxford Mail investigation has found traces of cocaine in public toilets in the city centre - prompting police to say they will increase patrols to catch drug users.

We discovered the illegal drug in city council-run toilets in Castle Street, next to the Westgate Centre, and at Gloucester Green bus station.

But out of seven other city centre loos in pubs and other locations we tested, only one - in All Bar One in High Street, - tested positive.

For the third time this year, we used Home Office-approved testing kits supplied by Didcot company Cozart.

Swabs were wiped over toilet cisterns, the backs of toilet seal lids and any other available surfaces where drug users could place lines of the white powder.

We targeted fewer bars this time and instead, surveyed shops, a theatre and council buildings.

City centre police chief, Insp Graham Sutherland, was aware of problems in the Gloucester Green toilets, but was surprised we found traces of cocaine in the Castle Street conveniences.

He said: "We were aware there have been rough sleepers and handbag thefts at Gloucester Green. We don't go into Castle Street, we weren't aware of problems there. I will brief my staff on these findings and up our patrols. It's always useful to know this activity is going on."

Mr Sutherland added: "There are some things that can be done to stop it. Some places spray WD40 on surfaces or a thin film of Vaseline but that can be damaging to clothing when people use the toilets."

Mr Sutherland said that since our checks earlier this year, many licensed premises had begun doing regular checks of toilets, and police officers inspected toilets as part of their Friday and Saturday night patrols.

All Bar One manager Gemma Black-Moore was not surprised, because she said staff had recently found a large quantity of cocaine in a cigarette packet.

She said: "We confiscated it and sent it to the police. Its owners asked us for it back and we asked them to leave, because we don't want that sort of clientele in the bar."

She said the toilets in the bar were checked every 30 minutes for suspicious activity.

City council spokesman Louisa Dean said: "We are grateful to the Oxford Mail for informing us about their discovery in our two public toilets.

"We have tried to discourage antisocial behaviour in our toilets, but it is very difficult to monitor usage in them."

In the first of our surveys in February, we found traces of the drug in seven out of 16 nightspots in Cowley Road, Jericho and the city centre.

In August, we found cocaine in 11 out of 16 venues.