Alliance Boots’ executive chairman Stefano Pessina is to become ­acting chief executive on completion of the merger with US pharmacy giant Walgreens. He will take up the role while a ­successor is sought for retiring Walgreens ­president and chief exec, Greg Wasson.

Pessina, who bought Boots alongside private equity group KKR in 2007, will head the enlarged business with a combined annual turnover of about £72bn.