Jackson, 27, is believed to have agreed a deal to play with the English Championship leaders, who are on course for promotion to the Premiership.

The fly-half was acquitted of rape last year but then had his contract revoked by the Irish Rugby Football Union.

His former Ulster coach Les Kiss and Ireland coach Declan Kidney are in charge at London Irish.

Jackson and his former Ulster and Ireland team-mate Stuart Olding were unanimously found not guilty following their nine-week rape trial last April.

But their Ulster and Ireland contracts were revoked because of social media and text messages revealed in court.

Jackson later signed for the Top 14 club, with Olding agreeing a deal with another French club Brive.

With Perpignan set for relegation after a poor season, Jackson is understood to have turned down the offer of a contract extension and appears to have plumped for a move to the Exiles despite approaches from other Top 14 clubs.

Jackson was given his Ireland debut by Kidney in 2013 and went on to win 25 international caps before his high-profile court case.

Following the court case, then Ulster Rugby chief executive Shane Logan said he "could not envisage" Jackson or Olding playing for the province or Ireland again.

However, IRFU performance director David Nucifora said last June that the duo could return to play for Ireland in the future.