BREXIT Secretary David Davis has threatened to quit if his cabinet colleague Damian Green is forced out over claims thousands of pornographic images were found on his work computer.

He reportedly told Prime Minister Theresa May "in words of one syllable" that he would find it difficult to stay in his job if the First Secretary was axed.

It comes as retired Scotland Yard detective Neil Lewis revealed he was "shocked" at the volume of material found in a 2008 raid on Mr Green's Westminster office and had "no doubt whatsoever" that it had been amassed by the Tory MP.

He stressed that none of the images were "extreme", but said analysis of the computer suggested they had been viewed "extensively" over a three-month period, sometimes for hours at a time.

Mr Green, who is the subject of a Cabinet Office inquiry into alleged inappropriate behaviour towards a young female activist, has denied looking at or downloading porn on the work computer.

The First Secretary of State - effectively Theresa May's deputy - declined to comment on Mr Lewis's allegations.

But friends of Mr Green said they were "gobsmacked" at the former detective putting his claims into the public arena and "outraged" at the decision to broadcast them.

And the Metropolitan Police Service (MPS) said it was launching its own inquiry about how information gathered during an investigation was made public.

Mr Lewis told the BBC he was involved in analysing the then opposition immigration spokesman's computer during a police investigation into Home Office leaks.

Although accepting that "you can't put fingers on a keyboard", he said a number of factors made him sure it was Mr Green himself who was accessing the "thumbnail" images.

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

"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."

The allegations echo claims made by former Met assistant commissioner Bob Quick, who Mr Green branded "tainted and untrustworthy" after he went public last month with his account of the material discovered in the raid.

Speaking to reporters at his Kent home, Mr Green said: "I've said I am not commenting any further while the investigation is going on.

"I have maintained all along and I still maintain – it is the truth – that I did not download or look at pornography on my computer, but obviously while the investigation is going on I can't say any more."

Mr Lewis said he had decided to speak out after contacting Mr Quick to offer his support when his former boss came under attack from Mr Green, who has accused him of "character assassination" to cause political damage.

He said he had always been "uncomfortable" about the outcome of the investigation into Mr Green and found his denial that he had looked at porn on his work computer "amazing".

Downing Street declined to comment on the latest allegations.

But Tory colleagues of Mr Green suggested the claims didn't stand up to scrutiny.

Crispin Blunt MP said a "busy shadow minister" would not have time to sit in his office "breezing through leisure websites of whatever type".

He said Mr Lewis' account "doesn't bear the slightest relation to the kind of life a member of parliament leads in the House of Commons".