Roche of Switzerland, best known for its valium sedative and locked in a battle for drug company supremacy with its Swiss rival Novartis, is preparing a fresh offer for Genentech, the US biotechnology company in which it owns a 56 per cent stake.

The bid, which is expected to be pitched at about $95 a share, is likely to be placed in front of Genentech’s board ahead of Roche’s year-end figures, due in early February.