On behalf of 34,000 specialist grades in the civil service and linked bodies, Hudd said: “Although the final package of reforms was accepted by members we made it abundantly clear to ministers at the time that the contributions increases being imposed between now and 2015 had nothing to do with pensions reform.

“The 3.2% increase in pensions payments represents a crude tax on our members on top of the wage freeze and the 1% pay cap. We wrote to the minister in March setting out our position and Prospect remains in dispute until this issue is settled.

“The union will consider its position on the pensions bill, and the dispute over pay exacerbated by the extra contributions over the next two years, at the next meeting of the Civil Service Sector Executive on 27 September.”