Police have revealed why officers in Epsom were out in numbers yesterday.

In a post on the Epsom and Ewell Surrey Police Facebook page, it said that they responded to reports of an incident involving a gang of youths, a kitchen knife and a shotgun in Epsom.

"The initial information that came into us was confusing but there appeared to have been an altercation between a named subject, a 17 year old male who was in possession of a knife, and possibly one or more other individuals," it read.

"We deployed local response teams, firearms officers and coordinated with our National Air Police Service (NPAS) colleagues who provided aerial support in their helicopter."

But things weren't as clear as first thought.

"Initial information suggested that someone had been 'stabbed' – but this was later altered to 'threatened' and a single witness claimed to have seen a 'shotgun', this was subsequently confirmed not to be accurate," the post added.

"The named subject was subsequently detained and arrested at his home under suspicion of possessing an offensive weapon, for affray, and for possession of a controlled substance - a kitchen knife matching the description given to our contact centre operators was found."