Cameron McKenna has won a startling victory over Clifford Chance (CC) in the race to be one of the Post Office's two principal commercial advisers.

Camerons, which has never worked for the Post Office before, was appointed to the lucrative panel along with Slaughter and May after an extensive review.

CC – one of the Post Office's principal legal advisers for 10 years – will be retained as back-up advisers, alongside Linklaters & Alliance, which is new to the panel.

Ten firms were actively considered for the panel and the bids included a presentation to legal services director Catherine Churchard.

Churchard said that she undertook a "vigorous" selection process and measured firms against objective criteria. She said that, although important, costs were not the main consideration.

She added that another factor was a good international presence. In a tacit endorsement of Slaughters' policy of maintaining close links with a series of leading foreign firms, she said this could be satisfied in a number of ways.

A spokesman for CC, which advised the Post Office on its acquisition of German Parcel earlier this year, said the firm was pleased to be retained on the panel in some capacity.

The government White Paper on the future of the Post Office is imminent and is likely to herald increased corporate activity and a move into the international arena.