Trade union representatives in the Civil Service are to face new curbs on the amount of time they can devote to union activities during work hours.

Cabinet Office minister Francis Maude will use the Conservative Party conference next week in Birmingham to unveil plans to restrict civil servants from spending more than half their paid time on union work.

The government is also set to impose a cap on the proportion of the Whitehall pay bill which can be spent on union representation.

According to ministers, 0.26% of the total pay bill goes on union representation, but under the new plans a maximum of 0.1% will be imposed on each government department.

Ministers say the measures, which go further than previously planned, will ensure value for money for taxpayers and bring the Civil Service into line with best practice in the private and wider public sectors.

However they are likely to further antagonise the unions who were angered by a speech by Mr Maude earlier this week in which he accused senior officials of deliberately blocking government polices they did not agree with.

A review exercise of the Civil Service ordered by Mr Maude found 6,800 representatives working on trade union duties with a further 1,000 officials working as health and safety representatives and 1,000 skills and learning representatives.

They include 250 so-called "pilgrims" - full-time union representatives funded by the taxpayer.

Under the plans, to be set out in Mr Maude's conference speech on Monday, any official spending more than half their paid time on union duties will require the specific approval of a minister, with the details to be published online.

Any officials who do continue to work full time for the union will be barred from further promotion in the Civil Service.

Union representatives will also not normally be given paid time off for union activities such as attending union conferences.

Government departments will be required to publish regular reports on their union representation arrangements, with new guidance being issued for line managers.

A Cabinet Office source said: "We recognise that trade unions play an important role in the modern workplace but we think trade union facility time arrangements in the Civil Service should reflect those in business and the wider public sector.

"For years under Labour there was insufficient monitoring of union activities. That's all going to change.

"Some civil servants have spent well over a decade doing nothing but trade union work and have even been promoted while doing so. That just isn't fair to the taxpayer or to other civil servants."