The facility at Barnard Castle, County Durham is competing with three rival sites to become the location for a new biopharmaceutical plant where groundbreaking drugs to tackle specific illness will be produced.

The decision has moved a step closer after a GSK project team visited the North-East to see if the facility, which employs about 1,000 workers, is suitable for the new investment. The other sites under consideration are at Irvine and Montrose in Scotland and Ulverston, Cumbria.

At the end of last year, GSK said it was planning a £500m investment in manufacturing after the Government confirmed it would go ahead with "patent box" tax reforms, which give firms a ten per cent reduction in corporation tax on profits from a patent registered and then manufactured in the UK.

Over the coming months GSK will ask the shortlisted locations to provide more information and further discussions are expected before a final decision is made early next year. Construction and commissioning will take about five years to complete.

"Wed planned the visit with military precision and everything went according to plan." Andy Cockroft, Barnard Castle site director said. "I am very proud of the way everyone on site presented themselves and the facilities. The visiting project team left the site with a very positive impression about the people, location and our case for the investment. We were really pleased with how the day went and whatever the outcome we will have enhanced our reputation as a site."

The regions bid was supported by Durham County Councils Chief Executive George Garlick and Head of Economic Development Sarah Robson as well as Bishop Auckland MP Helen Goodman.

Mr Cockroft added: "Having key stakeholders join us for part of the meeting really helped demonstrate how much local support there is for the site. Were very grateful to everyone who has helped us."

GSK has invested more than £80m at Barnard Castle since 2006, and is spending a further £25m this year upgrading and investing in buildings and machinery.