IllicitEncounters.com is a UK online dating service for married people. The site was founded in 2003, by entrepreneur Stephen Lines. Currently, it is the UK's largest extramarital dating website, with a reported 900,000 members.
The website was founded by businessman Stephen Lines. In an interview with the Daily Express in April 2010, the wife of current CEO Adam Scott, Kim Scott, described how the former owner decided to rebrand his failing singles site.
“Lines ... came up with the idea after he and his wife hosted a dinner party and one friend, after too much wine, confessed the same illness that had kept her husband away from the party that evening had also put paid to their sex life. She confided she was desperate to get her sexual thrills elsewhere, without compromising her marriage. It gave Lines the idea to overhaul his ailing mainstream dating site ... by facilitating affairs instead”.
The company has been banned from advertising on several occasions. In an interview with Campaign magazine, CEO Adam Scott said that the website had “struggled to secure commercial spots in the mainstream media, having been refused permission to advertise by some magazines and broadcasters”.
In May 2010, Ratcliffe Fernley Media, owners of Titan Bus Advertising, cancelled the site’s planned campaign, which was scheduled to run across 22 buses across London, Manchester, Liverpool, Bristol, Leicester and Nottingham. Despite having explicit go-ahead from Rodger Fernley himself, Lisa Radcliffe, finances director of Radcliffe Fernley Media, commented that "We are not saying the site should not be advertising but we choose not to advertise that kind of activity on our fleets. We are proud of our relationships with our bus companies and do not want to upset them.".
Since its conception IllicitEncounters.com has produced several large, independent studies which have served to explore the finer points of infidelity. The site's 'Sex and Marriage' survey, conducted via British research body OnePoll and released in March 2010, quizzed 4,000 UK spouses on their extramarital habits. The results found British county Devon was the most adulterous county in the UK, with over 48% of respondents from the area admitting to cheating on their current partner. This survey also gave a definitive list of Britain’s Top Ten Cheating Counties.
The site has also released large-scale internal studies, which focus on trends in the behaviour of cheating spouses. In August 2010, one study found that British men were twice as likely to be caught cheating than their female counterparts. The study also showed that text messaging was the method by which British spouses were most likely to be caught cheating.
In January 2015, a further study by IllicitEncounters.com revealed 5 January as the biggest day of the year for affairs, as this is typically one of the first days back at work and people take the opportunity of additional time away from their spouse to explore affair opportunities. 
- Ashley Madison, a Canadian online dating website aimed at married people
- Sadie Nicolas, 'Married to the Marriage Wreckers'. Daily Express, April 30, 2010.
- "Costa Revealed As The Coffee Shop Venue Of Choice For People Committing Adultery". The Huffington Post UK. 2013-11-20.
- Williams, Matt (April 27, 2010). "Extra-marital dating site seeks creative and media buying agencies". Campaignlive.co.uk.
- "Last Minute Ban on Nationwide Affairs Campaign". Marketing News Today. May 5, 2010.
- McCabe, Maisie (May 5, 2010). "Extramarital website has bus ad banned". Brand Republic.
- Bowser,, Jacquie (July 9, 2009). "Married dating website banned from advertising on London cabs". Brand Republic.
- "Sex In The UK : Top 10 Counties For Being Unfaithful". The Metro. March 25, 2010.
- Quigley, Rachel (August 13, 2010). "Men, the Love Cheat Losers". The Daily Mail.
- "January 5th – The Biggest Day Of The Year For Affairs?". ONS Blog. 2015-04-20.