Adecco, the Switzerland-based temporary staffing group, is poised to regain its investment grade credit rating after Standard & Poor's, the ratings agency, changed its outlook on the group to positive from negative.

Analysts had been expecting both S&P - and rival agency Moody's - to hold their ratings firm or even lower them further after the group twice failed to publish annual accounts and launched a probe into "irregularities" at its North American subsidiary Adecco Staffing.