A cannabis factory with £30,000 worth of plants was raided by police today after being spotted by a member of the public.

About 200 cannabis plants - some had recently been harvested, it is believed - were discovered when police broke into the rented three-storey house in Headington Road, Oxford, at 8.30am.

The raid came 15 minutes after officers received a tip-off, but police refused to comment on the source of the information.

Pc Chris Miles said the set-up appeared "less professional" than previous cannabis factories discovered in the city. However, he thought it might have been operated by the same Vietnamese growers who were previously thought to have downscaled their operations.

Pc Miles said: "The set-up in this house is almost identical to the houses that were raided last year, which we thought were being operated by Vietnamese gangs.

"Previous houses that we raided were normally very neat, but in this case, it is very messy and doesn't appear as professional.

"Another thing that was interesting in this case was that none of the windows on the ground floor had been blacked out."

It was this that led to police forcing their way into the house through the back door after they spotted a ventilation tube hanging down into the hallway from upstairs.

Pc Miles said: "As soon as we stepped into the house, we could smell the cannabis."

No-one was inside, but there were signs someone had stayed at the address recently and that a harvest had been just been carried out.

Pc Miles said: "This could have been done in the last couple of days, but it's hard to say. It would have been nice to have made some arrests, but we are disrupting their operation."

A neighbour said he had seen South East Asian men coming and going from the property, but assumed they were students.

Neighbour Oliver McVeigh, 20, a student at Oxford Brookes University, said: "I saw a really tall Asian guy and a shorter guy coming and going on a few occasions. One of them drove a really nice dark blue BMW - I just thought he was a well-off international student.

"I was shocked when the police knocked on the door, but when I think back, I did hear a lot of drilling noises when I first moved in."

James Lukas, 21, also a student at Brookes, said: "The first I knew about it being a cannabis factory is when I heard the police smashing the window this morning."

Leigh Thompson, Oxford police's drugs co-ordinator, estimated the haul was worth £30,000.