Pornography described as extreme found on the deputy prime minster's computer would have been illegal if it had been discovered just weeks later, it has been claimed.

The computer was seized in a raid on the deputy PM's office in November 2008 during an inquiry into government leaks.

Some images found on the system were said to be so vile that police took advice from the CPS on whether to prosecute.

But they were told there was no relevant law was in place when Mr Green’s office was raided.

The computer was seized in a raid on the deputy PM's office in November 2008 during an inquiry into government leaks. Pictured, Damian Green (left) and the prime minster (right)

The law was changed eight weeks later, in January 2009.

A source close to the investigation told the Sun: 'Porn was being accessed on an almost virtual daily basis. Police were told nothing could be done.

'Quite simply, it was not illegal to be in possession of extreme images before January 2009.

'If the raid had happened a few weeks later it would have been.'

The First Secretary of State is clinging to his job as he faces a Whitehall 'sleaze' inquiry after a female journalist said he 'fleetingly' touched her knee two years ago.

He said of the latest claim last night: 'As I have said throughout I did not put or view pornography on the computers taken from my office.'

It is unclear who could have downloaded the porn. It did not feature sexual images of children.

Accessing extreme porn became illegal under sections 63 to 67 of the 2008 Crime and Immigration Act which came into force on January 26, 2009.

The 2009 law made it illegal to possess images featuring acts which threaten life, cause serious injury to a person’s private parts or depict sex with animals or a corpse.

It came into force following a four-year campaign by the parents of murdered Jane Longhurst.

Her killer Graham Coutts, 46, of Brighton, had a strangulation fetish and accessed violent images of simulated murders and rapes.

Mr Green has previously said police never told him that any improper material had been found on a parliamentary computer.

He also also denied making any sexual advances to the journalist Kate Maltby.