The company will today announce its end-of-year results when it is also expected to make an announcement about its continuing restructuring programme.

It is thought that cuts will be made in its US and European operations.

The Montrose site, which employs 280 full-time staff, manufactures six active pharmaceutical ingredients for GSK's respiratory and HIV products.

It is also the only site in the world licensed to manufacture zanamivir, the active ingredient in its anti-flu inhaler treatment Relenza. Last year GSK invested £5million in manufacturing facilities at the Montrose site to help double its output of zanamivir to meet increasing demand worldwide amid fears of a swine flu pandemic. It brought the investment in the factory as a whole to £40million over the last four years.

The company, however, will today update on flu vaccine sales which are lower than initial expectations due to the resulting mild pandemic and cancelled orders from government agencies.

It was aiming to boost production to 190million doses by the end of last year, with 10.6million supplied to agencies within the UK. Between April and June last year sales of Relenza, which was also produced in the form of an injection for serious flu patients, rocketed to £60million. The previous year's sales amounted to £3million.

A company spokesman said: "We have these results coming out but wouldn't comment beforehand. This is press speculation and if there was any effect on our employees we would speak to them first."

As well as 280 permanent staff, the factory employs around a further 120 contract staff and is one of the biggest manufacturing businesses in Angus.

Its new £5million facility was opened in November by First Minister Alex Salmond. At the time site director Dave Tudor said the Montrose site was strategically important in terms of meeting the specific challenges presented by the flu pandemic and the contribution the pharmaceutical industry makes to the national economy.