The Metropolitan police commissioner has revealed he tried to find out if dogs could be used to search for knives.
"We have dogs that can search for drugs passively," Sir Bernard Hogan-Howe said at a London Assembly meeting on Thursday.
"I've tried to find out whether we can get dogs to search for knives … they told me it's impossible. You can do it for guns but you can't do it for knives… But we have tried."
In a statement to BuzzFeed News, the Met later said it had "consulted with scientific experts about the use of dogs to find knives and was informed it would not be feasible."
An expert at the RFA security firm told BuzzFeed News that it would be "very difficult" to use dogs to find knives in stop-and-search operations.
"If its just a plain metal blade, its going to be very difficult because metal in itself doesn't give off a scent," he said.
"Even with firearms, its not the actual metal you're looking for, it's the associated parts that go with it. For instance, gun oil and gun-cleaning products."
After years of decreasing, this year knife crime has risen by 18% in London, the Metropolitan police said. This is thought to be caused by a reduction in stop and search, and an increase in the availability of knives from illegal websites, The Guardian reported.