The takeover bid Pfizer is preparing to mount for AstraZeneca has just taken an interesting turn.

Until now the cross-party, political consensus surrounding the idea of the US pharmaceutical giant buying control of its British rival has been, crudely put: "Fine in principle although we do want reassurances."

Lord Sainsbury, the billionaire of supermarket fame, has told the Financial Times that under no circumstances should any deal be allowed to go ahead.

He told the newspaper that a takeover by Pfizer would be a "devastating blow to our profile in the pharmaceutical area, which I think is going to be critical in the next 30 years".

His view is that AstraZeneca is an asset that is too economically precious to be allowed to fall into foreign ownership.

He says that the British government, which has this week held a series of meetings with the chief executive of Pfizer to discuss the implications of any bid, should make it clear that it is "undesirable".

This is a significant intervention. Lord Sainsbury's voice will resonate.

He is a former Chairman of the family business, a former Minister of Science in the last Labour government (a post he held for eight years), the current chancellor at Cambridge University and a Labour peer.

Lord Sainsbury (right) pictured with Gordon Brown in 2007. Credit: PA

His influence on Labour policy was obviously at its most pronounced under Tony Blair, when he was also a generous donor, but sources within the party I have spoken to tonight suggest that its attitude towards any bid that Pfizer might make is hardening.

The talks with Pfizer this week have been lead by the Cabinet Secretary, Jeremy Heywood, on behalf of the government.

Vince Cable, George Osborne and David Willetts have all spoken with the company's chief executive, Ian Read.

Ministers want a cast iron commitment from Pfizer to AstraZeneca's operations in Britain, specifically the existing plan to move its headquarters to Cambridge.

Pfizer has already made comforting noises but my understanding is that it is unlikely to be willing to sign anything that resembles a legally binding agreement.

Lord Sainsbury told the FT that any reassurances Pfizer makes would be "frankly meaningless".