A family of four were robbed by two masked men on a moped as they sat in a stationary car in Croydon, south London.

One of the suspects threatened the family with a large knife on Keats Way, Coulsdon, at about 17:45 BST on Friday.

Police say the pair made off with a “small quantity of jewellery”.

A 30-year-old woman suffered a cut to the hand during the robbery, as one of the suspects attempted to steal her bracelet. It is believed that the other man also had a knife.

Detectives described the suspects as two white males, aged in their late teens or early 20s. Both were of slim build and wore dark coloured tracksuits, black crash helmets and facemasks.

The number of offences carried out by criminals using mopeds in London has increased from 827 offences in 2012 to more than 23,000 last year. Data obtained by the BBC showed during that period, more than 40% of such offences happened in just two boroughs – Camden and Islington.