Jacqui Smith has revealed she felt "frozen rather than angry" when told her husband had entered a parliamentary expenses claim for pornographic films.
The former Labour home secretary told Radio Times she felt "protective" towards Richard Timney, despite the episode ending her political career.
Ms Smith said she had not gone "through the expense form closely enough".
She also told the BBC she was "worried" about the availability of porn on the internet and the lack of restrictions.
Ms Smith, one of the first MPs to have their expenses claims published by the Daily Telegraph in 2009, has carried out an investigation of the pornography trade for BBC Radio 5 live.
'Pushing the boundaries'
She told the station what was most "worrying" was the availability of porn, particularly on the internet - where she said there were "very little restrictions".
"We are a very long way from the days that people passed a video around or had a magazine under the mattress. The extent to which, unregulated or without any need for proof of age, people of all ages can look at porn pretty much, day in, day out, for hours on end on the internet."
In seeking to analyse the impact porn had on society, Mr Smith said she found that those working in regulated areas of the trade were, in her opinion, largely "trying to be responsible".
"One of the most interesting things I found is that the people who actually work in the industry - I found I liked them more than I thought I would, I found them pretty frank and open."
But Ms Smith, who said she had not watched any of the films her husband had claimed on expenses, said the real threat came from unlicensed material in which people were trying to "push the boundaries".
"The problem is the stuff that is so easily accessible which is way outside that regulation," she said.
'I was wrong'
Among the items for which reimbursement was claimed were two pay-per-view pornographic films watched by Mr Timney, who ran his wife's constituency office.
But Ms Smith, the first-ever female home secretary, told the Radio Times that when she heard the news she "was more frozen than angry. I just couldn't believe that we - both of us - had put in this claim."
She added: "I was the one who did the wrong thing. For claiming it. For not going through the expense form closely enough."
She said she had decided to quit because of concerns for her family and had not been asked to step down by the then prime minister Gordon Brown.
The incident had left her husband "devastated", she said. "Really, deeply affected by what it did to me and the family."
Ms Smith denied suggestions that the pornography had been watched by her son, with her husband taking the blame.
Despite outlawing violent pornography while she was home secretary, she said she was "shocked" at the amount of hardcore material still available on the internet.
Asked if her husband had known about this, he might not have chosen pay-per-view films, she replied: "Yes, that's what my 17-year-old son said: 'Dad, haven't you heard of the internet?'"
In October 2009 Ms Smith apologised in the House of Commons for breaching expenses rules by listing her sister's house in London, which she shared, as her "main home" and then claiming second home allowances on her Redditch family home.
A standards inquiry found that she had "wrongly" designated her home but had followed officials' advice at the time.
Ms Smith lost her Redditch seat to the Conservatives last May, having served as its MP for 13 years.
Her documentary, Porn Again, will be broadcast on 5 live on Thursday, 3 March at 2130 GMT.