How MI5 caught UK embassy spy selling secrets to Russia

A spy at Berlin's British embassy, who sold secrets to Russia and was caught in an undercover MI5 sting, has been jailed for 13 years and two months.

David Smith, 58, tried to damage Britain's interests by passing on details of the embassy and its staff for cash payments, a judge found after the spy pleaded guilty.

The BBC's Home Affairs correspondent Tom Symonds explains what Mr Smith did, and how he was stopped.