A former police detective who examined deputy prime minister Damian Green's office computer has spoken of how he was "shocked" at the thousands of pornographic images which had been downloaded onto it.

Pressure continues to mount on the Tory MP regarding his conduct following the claims which stem from when officers seized his Commons office computer in 2008 during an inquiry into government leaks.

Former Scotland Yard detective Neil Lewis has now spoken about how there were "thousands" of legal thumbnail pornographic images on Green's computer.

A check on the computer's internet history also showed pornography had been viewed "extensively" over a three-month period, with some websites being searched for and viewed for several hours.

Speaking to the BBC, Lewis has said there is "no doubt whatsoever" that it was Green who was viewing the pornography at his computer when he was an opposition immigration spokesperson at the time.

Lewis said: "The computer was in Mr Green's office, on his desk, logged in, his account, his name.

"In between browsing pornography, he was sending emails from his account, his personal account, reading documents... it was ridiculous to suggest anybody else could have done it."

He added: "The shocking thing as I was viewing it, I noticed a lot of pornography – thumbnails, which indicated web browsing. There was a lot of them. I was surprised to see that on a parliament computer. I had to take a step back because I wasn't expecting that."

Lewis also played down previous reports that some of the images were so extreme or violent they were classed as illegal just a matter of weeks after the computer was seized and assured none of them showed children or signs of abuse.

Green denies the claims and said he has never watched or downloaded pornography on the office computer.

A spokesperson for Green said: "It would be inappropriate for Mr Green to comment on these allegations while the Cabinet Office investigation is ongoing, however, from the outset he has been very clear that he never watched or downloaded pornography on the computers seized from his office.

"He maintains his innocence of these charges and awaits the outcome of the investigation."

The details surrounding Green's computer arrived after an investigation into the Tory MP was launched after he was accused of sexual misconduct by journalist Kate Maltby, allegations he described as "untrue and deeply hurtful".

Damian Green
Damian Green denies downloading or viewing porn on his office computer Carl Court/Getty Images