Justin Harrison has left Bath with immediate effect after requesting an early release from his contract. It is understood that the former Australia lock has pre-empted the results of an internal misconduct investigation and left the club.

Bath's chief executive, Bob Calleja, launched the inquiry on Sunday after allegations that a number of the squad were involved in a fracas with Harlequins players at the club's end-of-season party. Bath, who have made no official comment, hope to complete the investigations within the next few days.

Harrison, 35, was contracted until the summer of 2010 but will return to ­Australia as soon as possible. The former ACT Brumbies and New South Wales Waratahs player joined Bath from Ulster on a one-year deal last summer. He signed a 12-month contract extension in December.

The alleged incident took place in a London pub on 10 May, the day after Bath's Guinness Premiership semi-final defeat by Leicester.

Bath are also investigating reports linked to drugs use. Last Sunday's News of the World reported claims that several players refused to provide samples for drugs tests following drinking sessions on the same weekend.

Four months ago the Bath and England prop Matt Stevens was banned from the game for two years after testing positive for cocaine.

A spokeswoman for the Rugby Football Union said: "We are aware of these particular allegations and are comfortable that the investigation process Bath Rugby is following is the right one for their club and their employees.

"At the current time we have not made any requests as part of that investigation in any way at all. When the investigation is complete we will review the findings with Bath and decide if further steps are required."