Private equity firms CVC, Kohlberg Kravis Roberts and Blackstone said on Friday they were in the early stages of assessing a possible bid for British supermarket group J Sainsbury.

Shares in Britain's third-biggest supermarket group leapt as much as 18% to an 8-year high of 526-1/2 pence, valuing the business at as much as 9.7 billion pounds ($19.1 billion).