Clifford signs on for more at Quins
"I am really pleased to have re-signed for this great club," Clifford said.
"I have been associated with Harlequins for close to ten years and I can't think of anywhere better to be as I continue to gain experience and develop my career.
"There are a number of influential and experienced players within the squad and I am looking forward to continuing to learn within such a competitive and highly skilled back row."
Having joined the Harlequins Academy structure aged 13, the former Cranleigh player has made close to 40 senior appearances for the club since his debut in 2012, scoring eight tries.
Close to the complete package, he has the ability to play across the whole back row. In recent years, Clifford has become a powerful ball carrier with an exceptional breakdown and set piece skillset.
While learning his trade through the Harlequins Academy, the back row forward represented his country at age grade level, captaining the 2013 Under-20 to Six Nations and Junior World Cup titles.
He was then selected to represent England Sevens during the World Sevens Series in Japan and Hong Kong.
Developing in recent years under the expertise of back row colleagues Chris Robshaw and Nick Easter, Clifford was named Supporters' Player, Players' Player and Young Player of the Season during the Club's 2014/15 End of Season Awards Dinner.
This season, Clifford was named as captain for Harlequins' European Rugby Challenge Cup match against Cardiff Blues and the six foot four forward is set to captain the club again this Saturday against Calvisano.
Confirming the news, Harlequins Director of Rugby, Conor O'Shea said: "Jack is one of a new breed of players coming through the system. For me he has the potential to become one of the very best players in world rugby.
"He has had to be patient with injury holding him back in recent times, but in the last 12 months he has begun to really kick on; I can see his graph continuing to rise in the coming 12 months.
"He knows the competition we have in our back row means he will have to be on his game every week. Jack has potential to be a great leader within the group and we will work at developing that side of his game too."
