Police officers discovered around one million indecent images of children at a house in east London, Scotland Yard has revealed.
It is the largest seizure The Metropolitan Police's Paedophile Unit has ever made from one individual, according to the force.
The haul, which included photographs and videos deemed to be of the most serious nature, was discovered by police at the Plaistow home of Robert James Barrow, 57.
He appeared at Southwark Crown Court yesterday and admitted offences of making and possessing indecent images of children, police said.
Barrow is believed to have amassed the "industrial scale" collection over a period of 15 years and shared them with other paedophiles, according to The Met.
He was arrested after admitting to officers that he had images stored on his PC before it was even examined.
Detective Inspector Noel McHugh, Paedophile Unit, said: "This is the largest seizure of indecent images of children that the Met's Paedophile Unit has recovered from one individual. Barrow's activities were on an industrial scale.
"This investigation demonstrates the commitment of the Met Police to target paedophiles both on and offline.
"This is not a victimless crime as each indecent image of a child possessed or distributed represents a child that has been abused in order that the image can exist."
Barrow admitted three offences under Section One of the Protection of Children Act 1978 relating to the making, possession and distribution of indecent images of children, according to police.
He is due to be sentenced on September 16.