The married dad, 29, bombarded the busty 22-year-old with pervy posts and begged for topless snaps.
He said last night: "I'd like to apologise to anyone this has offended."
The fan sent sexy Twatter messages by clean-cut TV favourite Manford said last night she was stunned to learn of his "sleazy side".
Debra McNamee was bombarded with pervy posts from Manford after contacting him through the social networking site.
The comic, whose third child with wife Catherine is due next month, began sending private messages and begged her to send him topless snaps.
He later also described in detail how he had performed a sex act while looking at them.
Debra, from Wolverhampton, West Midlands, said: "Jason's got a reputation as being very clean-cut - but there's obviously a more sleazy side to him too.
"I was really shocked by the way he pursued me and I think most people will be too. If I were his wife today I'd be furious."
Manford took over his BBC1 role from Adrian Chiles last July and is one of the most prolific Tweeters in showbiz with more than 200,000 followers - many of them young girls.
He first met Debra online on October 22 when she posted a message on his official Twatter page.
A day later the star, dad to twin one-year-old daughters, began sending her private messages and excitedly asked her to send him racy photos.
Five days later, on October 28, the fan finally caved in and sent him two pictures of herself in a lacy bra and one of her posing topless.
Manford's last burst of sleazy messages was sent shortly before 2am on the morning of October 30 - hours after a gig in Bradford, West Yorks.
Debra said: "When I first sent a message to him I thought he'd never reply. Famous people never do and I was surprised when he got in touch.
"At first he just asked me about my dog and what I was up to and things like that. But after a while it started to get a bit more flirty."
She added: "When he thought no one would know, he started getting more and more racy in what he said.
"I think he was bored on tour and thought he'd never get found out. He'd ask me for photos and then tell me how excited he was by them.
"He asked me if I could keep it secret and he told me I looked sexy.
"It made me feel good, but I was quite shocked about what was going on. It was very different from how he seems on the TV and on stage.
"I'm a big fan of his and I think I just got caught up in the excitement of Tweeting someone so famous."
Manford, famed for his family-friendly image, appeared on The One Show with co-host Alex Jones yesterday. But before going on-screen he confessed to his Twatter antics.
He said: "I can see now that what started out as a bit of messing about and having a laugh on Twatter has been misjudged and I'd like to apologise to anyone that this has offended as that was the last thing I ever intended to do."
A source added: "Jason is deeply sorry and horrified at the upset he's caused his family and his wife.
"He's had a meteoric rise to fame and it's clear now the stardom has gone a little bit to his head. His wife and the BBC bosses will be rightly furious about his behaviour."
Heavily-pregnant wife Catherine, 29, was not at the couple's £650,000 six-bedroom pad in Stockport, Cheshire, last night.
The actress wed Manford in October 2007, but they have never revealed their daughters' names for reasons of privacy.
Earlier this year, Manford declared: "I share so much of my family with stand-up and Twatter and stuff that I just want to keep a bit of it private.
"The fame side doesn't interest me and I'd rather not have that."
In February, The Sun revealed how Family Fortunes host Vernon Kay, 36, sent racy texts and Twatter messages to Page 3 beauty Rhian Sugden - behind the back of his telly presenter wife Tess Daly, 41.