Britain's main civil service union is set to take legal action against the government unless ministers show they are "serious" about closing the pay gap between men and women.

The Public and Commercial Services Union issued the warning when releasing figures showing a 27 per cent pay gap between male and female full-time civil servants.

"This a government that likes to lecture everyone about family friendly policies but while treating its own staff probably worse than many other employers," said PCS chief, Mark Serwotka.