Cyclists in Oxford are being warned to lock up their bikes and even remove the saddles after a spate of thefts.
The numbers of bicycles being stolen has been going up steadily since the summer, with 16 taken in November in East Oxford alone.
Insp Brian Cooper, East Oxford police inspector, said: "If you have children, get them to take responsibility for their bikes and even think about taking off the seat and taking it with them.
"We recently did a raid on a house within the local area and they appeared to be stock-piling pedal cycles and we did find a number of stolen bikes."
Insp Cooper said the theft of bikes was being taken very seriously and officers were taking extra measures to try to track down the culprits.
He said: "People should expect to get stopped and they should be expecting to be asked: "Is it your bike, where did you purchase it from and have you got proof of purchase?
"We are having a crackdown on cycle crime not only to recover stolen bikes but to find the thieves and deter them - they are within our sights."
He said one of the problems was that many modern bicycles had quick release mechanisms on the wheels and the seats.
Insp Cooper said: "If people have got expensive bikes, particularly with quick release mechanism, if they lock the frame, we are finding the wheels and saddles get stolen.
"People also need to think about where they lock up their bikes - especially if they have got an expensive one.
"They need to think about carrying more than one lock and using two or three locks to secure the main parts to the bike and the bike to a bike rack. Lamp posts are probably not good enough."
But he warned a number of the thefts were happening because people were simply not bothering to lock up their bikes at all.
He said: "I spoke to one woman who left a bike outside a shop and was inside for maybe 20 seconds and it was stolen.
"It only takes one second to pull a bike off a shop window, get on it and ride away."
He said officers would continue spot checks in streets.
They would stop every single cyclist to check that they owned the bicycles they were riding.
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