Police who spent four years hunting a man they have called a "prolific and depraved offender" have released footage of him being arrested.

Dr Matthew Falder, a geophysicist at the University of Birmingham, can also be seen in surveillance footage captured by the National Crime Agency, which worked with police forces around the world to discover his identity.

Falder, a University of Cambridge graduate, has admitted 137 offences. He sought out victims online and hid from the authorities using dark web paedophilia sites and email encryption.