Four 'big-name' stores in the borough of Hounslow were yesterday caught selling knives to children aged under 18 in a major crackdown on knife crime.

The shops fell foul of the law in a sting operation carried out yesterday by Hounslow Police Cadets as part of the London-wide Operation Big Wing.

Hounslow Police, which initially tweeted that only two stores had been caught out, has not named the companies but said they would be referred to Trading Standards.

Officers also recovered a knife yesterday during a search of the Brentford Towers estate, in Green Dragon Lane - one of many weapons sweeps taking place across the borough.

An outstanding arson suspect was also arrested during the day of action, and one person was arrested for money laundering in Hounslow West.

Chief Inspector Rob Weir, who led the operation in Hounslow, said a total of 17 arrests were made during the day for offences including handling stolen goods and possession of drugs.

Police also issued their first warning for possession of khat since the drug became illegal on Tuesday.

"All these underage knife purchases were at well-known stores rather than smaller local stores, which is normally the case with test purchases of alcohol," said Mr Weir.

"This suggests some of the bigger stores need to improve awareness among staff about the rules when it comes to selling knives."

Across London, 140 arrests were made during the morning alone as part of Operation Big Wing.

They included a man arrested in Hillingdon on suspicion of three recent knife-point robberies in West Drayton and a 15-year-old caught with a knife in his underpants in Islington.

Yesterday's crackdown follows a spate of stabbings in the borough, which led Feltham & Heston MP Seema Malhotra to call for a summit on youth violence.

In March this year a man was arrested after a gun and drugs were found at a home in Isleworth as part of Operation Big Wing.