Williams left the field with fake blood pouring from his mouth against Leinster
Harlequins chairman Charles Jillings has resigned after accepting ultimate responsibility for the 'Bloodgate' affair that has disgraced the club.
Tom Williams faked injury to allow fly-half Nick Evans to return to the field in a cup tie and director or rugby Dean Richards has since stood down.
"Harlequins acknowledge that we failed to control Dean Richards," said Jillings in a statement.
"As a result of the board's failure to control Dean, the club cheated."
The incident happened in a Heineken Cup match against Leinster and led to an initial 12-month ban for winger Williams that has now been reduced to four months.
Richards has been banned from coaching worldwide for three years for his role in the fake blood injury.
As chairman I am ultimately responsible for all decisions
His ban is particularly severe because the investigation revealed he had been involved in four similar incidents.
Quins themselves were fined £259,000 and physiotherapist Steph Brennan was also handed a two-year ban.
And in a lengthy statement on the club's website, Jillings added: "As chairman I am ultimately responsible for all decisions.
"I apologise unreservedly to all our stakeholders for inadvertently compounding the issues. The escalation of these issues in the public domain needs, I believe, a clear response.
"In this context I have decided to resign as chairman and director. Ultimately this happened under my watch, and the failure to control must fall at my door."
Williams has claimed he was offered a new four-year contract and other benefits by club officials if he kept quiet about the involvement of others in the incident, which took place during the quarter-final at The Stoop on 12 April.
During the game, Richards ordered Williams to feign injury by chewing a fake blood capsule to allow goal-kicker Evans to return to the field.
Williams later had his lip cut in an attempt to make the injury appear genuine, but following an investigation by the European Rugby Cup (ERC), who oversee the Heineken Cup, the 26-year-old admitted what had happened.
"This is totally unacceptable," added Jillings.
"The board was unaware of these facts until Tom Williams came forward on Wednesday 29th July, after the initial ERC Hearing.
"I returned from holiday on 3 August to address the findings of the ERC hearing. I was faced with the full extent of the devastating revelation that we had cheated and lied in our statements."
Malcolm Wall has been appointed chairman of the club on an interim basis.
Wall was previously chairman between 1997 and 2000 and has been conducted the board's internal review since the initial European Rugby Cup judgement into the fake blood incident.
"I hope to work with the board and management team to build on his legacy, to put this sorry episode behind us and rebuild the reputation of the club," said Wall.