The pair launched Gifford McCrystal in February 2005 but are understood to have been operating increasingly independently.
Gifford, who in 1980 co-founded GJW, has been working separately on international oil PR assignments picked up since quitting the firm in 2003. GJW became part of Weber Shandwick after a series of acquisitions.
McCrystal, a former diarist at the Evening Standard, Telegraph and Observer, is understood to have been plying his trade by using UK business contacts accumulated in his time as a journalist.
Both Gifford and McCrystal declined to comment.