21-year-old Collier learned his rugby at Cranleigh School in Surrey before joining the Harlequins Academy in 2008. The Hammersmith born prop forward has represented England at Under 16 and Under 18 levels and was a member of the Under 20 team that qualified for the IRB Junior World Cup final in 2011.

19-year-old Sinckler began playing rugby at Battersea Ironsides RFC and represented South-East London at Under 16 and Under 18 levels before joining the club's Academy. He has also represented England at U16, U18 and last season at U20 level for the 2012 Six Nations and Junior World Championships.

Both players have already made their senior debuts for the club.

Harlequins Head Coach, John Kingston said, "I am absolutely delighted that Will and Kyle have re-signed. Both have already had exposure in the first XV and I have no doubt that over the coming seasons both players will make a great impact in the Premiership.

"Their development through the club's Academy is once again proof of Harlequins' considerable ability to nurture young English talent."