Vaccine company PowderJect Pharmaceuticals is believed to be set to reject a takeover bid by its US rival Chiron.

The company, which employs several hundred people at Oxford Science Park, Sandford, confirmed it had received a number of approaches.

The firm, which earlier this year was embroiled in controversy over political donations, said it had received preliminary approaches from "certain parties".

The brief statement added: "It is too early to say whether these might or might not lead to an offer being made for the company."

PowderJect said a further announcement would be made in due course and did not name any potential suitors. But a report in the Financial Times said PowderJect had received a £455m indicative bid from US rival Chiron, which it was planning to reject as "opportunistic".

A string of bad news has rocked PowderJect's value over recent months. It was awarded a £32m contract to supply the Government with smallpox vaccine this year, which would be used in case of a bioterrorist attack.

But it was subsequently discovered that chairman and chief executive Paul Drayson had given the Labour party £50,000 only a few months earlier.

The Government said the contract was not put out for open tender for security reasons and Mr Drayson denied there was a link between donation and deal.

But the group was then rocked further, with £90m of its value wiped out in one day, after it recalled its tuberculosis vaccine.

A licence for the product in Ireland was temporarily suspended after "potency problems".

The TB problem is predicted to knock £5m from profits and shares have fallen from highs of 603.5p at the start of the year to Friday's close of just 255p, giving PowderJect a market value of £232m.

The Financial Times said talks between Chiron and PowderJect began this month. The US firm was reported to have made a verbal offer although a written bid has not yet been submitted.