A former trainee police officer has been jailed for 15 years for rape and a string of sex crimes against girls as young as 13.

Mohammad Arshad, who "harvested" young victims from social media sites, was a trainee police officer in 2014.

The 35-year-old from Luton was suspended when the mother of one of his victims came forward.

He was found guilty of 17 offences against 12 victims over a two-year period following a trial last month; convicted of nine counts of causing a child to engage in sexual activity; three of sexual activity with a child; and two of meeting a child following sexual grooming.

He was also found guilty of one count each of rape, causing a child to watch a sexual act, and paying for the sexual services of a child.

He was found to have "hundreds" of details of young girls, mainly from the Luton area, and was "obsessed with turning as many contacts with these young girls as possible into sexual encounters", Judge Jonathan Carroll said.

Jailing him for 15 years, with an eight-year extended licence period, at St Albans Crown Court, the judge said: "Between 2007 and 2013 you were actively and obsessively engaged in harvesting young girls' data from various social media sites, including BlackBerry Messenger, Facebook and WhatsApp."