GlaxoSmithKline plans £275 million of new investments at three drug manufacturing sites in Britain, signalling its confidence in the country despite last month’s vote to leave the EU.

Britain’s biggest drugmaker, which had argued against Brexit before the referendum, believes the UK remains an attractive place for making medicines, thanks to a skilled workforce and relatively low tax rates.

The country’s so-called patent box boosts profits from patented innovations by halving the rate of corporation tax. This tax relief, which favours pharmaceutical companies, has come under fire in recent days from the opposition Labour Party.

GSK said yesterday it was investing in sites at Barnard Castle, in the north of England, Montrose, in Scotland, and Ware, north of London. It plans to increase production of next-generation respiratory drugs and biotech medicines.

The vast majority of these products will be exported.

“It is testament to our skilled UK workforce and the country’s leading position in life sciences that we are making these investments in advanced manufacturing here,” said chief executive Andrew Witty.

Business minister Greg Clark said GSK’s move was a clear vote of confidence in Britain and demonstrated that “there really is no place better in Europe to grow a business”.

The company has a large part of its global research and manufacturing cost base in Britain, even though nearly all its sales are generated overseas.

Witty, who is retiring next year, had said before the vote that Britain should remain in the EU, due to fears that Brexit could disrupt Europe’s unified system for drug regulation and hamper access to top scientific talent.

Despite this, the company, which will be helped by recent falls in sterling, has concluded that the country remains a good place to do business.

Britain accounts for nearly half of GSK’s worldwide research and development and around a third of its manufacturing. It has a total of nine UK manufacturing sites employing some 6,000 staff.