Gerard Collins, 27, was arrested after his detective lover Graham Ferguson, 41, was found with a lewd DVD in his office, jurors were told.
Southwark Crown Court heard a search of their London home uncovered a laptop, floppy disk and CD containing similar images.
But Collins, who works for the British Transport Police in the counter-terrorism unit, told the jury: “I like men much older than me, of larger stockier build, kind of like a daddy type.”
Collins, awarded a commendation following his work during the 7/7 bombs at Kings Cross Station, said his five-year relationship with Ferguson was his “first serious one”. “Before Graham I had relationships with men aged 38, 42 and 50.” Collins, originally from Co Cork, said he realised he was gay when he was 21.
“I think it was always in the back of my mind, but I didn’t realise exactly what it was until I came to terms with it,” he said. “I guess the norm in Ireland was that you were a straight man and that was it.”
He told the court within the gay community his preferred type of men were known as “daddy, bear and sometimes silver daddy”.
Ferguson was working in a Met Police department specialising in investigating corrupt officers and was on sick leave when a colleague found a DVD containing short films of children being sexually abused in an unlocked filing cabinet.
The horrified officer, who worked alongside Ferguson at the Director of Professional Standards building, in Jubilee House, Putney, reported his find to his manager.
Fellow officers from his department then went to search the couple’s flat where further material was found.
Collins admitted downloading vast quantities of gay porn on their shared computer but said had he known there was any images of children on it he would have deleted them.
He said he would download homosexual pornography “in bulk” and set the computer up to store the images overnight from websites such as “daddy swap”.