The FTSE 100 giant has been fighting HMRC on transfer pricing issues and controlled foreign companies problems since 1994, but has lost patience with the taxman and threatened legal action in efforts to force the taxman’s hand.

GlaxoSmikthKline said: ‘HMRC has not yet formalised claims in respect of these matters and GSK is seeking to resolve them in discussions with HMRC.

‘There continues, however, to be a wide difference between the group and HMRC positions, which may ultimately need to be settled by litigation.’

The warning that court action may be the only way to settle the issues may be embarrassing for HMRC, which has made great play recently of its attempts to resolve long-standing tax issues more quickly.

GSK is also taking on the Canadian, US and Japanese tax authorities. The company said: ‘The integrated nature of the worldwide operation gives rise to complexity and delay in negotiations with authorities as to the profits on which individual Group companies are liable to tax.

‘Resolution of such issues is a continuing fact of life for GSK.’

HMRC said that it could not comment on individual cases.