A sex offender has been jailed after being caught by plain clothes British Transport Police officers assaulting a teenage girl on the London Underground.

Abdulrizak Ali Hersi, 32, and of Invicita Close, Limehouse, was found guilty of sexual assault at Inner London Crown Court on 5 May.

The judge sentenced him to 18 months in prison and a ten year Sexual Harm Prevention Order which prevents him from intentionally standing behind or next to any female he doesn’t know in a public place.

He was also ordered to pay a victim surcharge of £187.

On 11 October shortly before 5pm, plain clothes officers on patrol on the Piccadilly Line observed Hersi board a train at Green Park and stand near the doors.

At the next stop a family got on the train and moments later Hersi sexually assaulted the 13-year-old daughter. Officers quickly intervened and took Hersi off the train at Leicester Square and arrested him.

Inspector Sharon Turner said: “Our plain clothes teams are specially trained in identifying dangerous sexual offenders like Hersi, who will do their level best to commit such crimes without notice.

“In this case, the victim and her family didn’t even realise what was happening until our officers quickly intervened.

“Passengers should feel reassured to know we have plain clothes patrols like this taking place across the Underground day and night to keep everyone safe. If you ever have any concerns while travelling please do text us on 61016.”