The 13-page offer received by Prospect and other Civil Service unions follows weeks of intensive negotiations with the Cabinet Office and the Treasury to finalise the details of a new scheme to take effect in April 2015.

Dai Hudd, Prospect Deputy General Secretary, said the final offer had made "significant progress" on the Heads of Agreement proposals tabled by the Government in December. But he stressed: "This offer only covers the new pension scheme to be introduced in 2015 and not the higher pension contributions being imposed from this year, which we continue to protest direct to the Treasury and ministers."

The new scheme is modelled on the scheme introduced in 2007 for new entrants to the Civil Service, called Nuvos, which already covers 20% of civil servants.

Compared to the Government's original proposals for change, the new scheme includes: a faster accrual rate (the rate at which pension is built up); a cap and a floor on the employer's contributions, to protect the interests of taxpayers and staff; additional flexibilities to give individuals more choice over their pension provision and date of retirement; and protection for the pensions of staff who are privatised or outsourced to the private sector.

However, unions were unable to improve on the amount of contribution increases being imposed on employees, which will average 5.6%; or the intention to align normal pension age with state pension age. A ruling on the unions' appeal against the CPI indexation switch is awaited any day from the Court of Appeal. 

The Government's proposals will now be considered by branch representatives from the union's Civil Service Sector at a briefing conference in London next Friday 16 March, before they are put to a ballot of all 34,000 members affected. 

Dai Hudd said: "This is a complex offer and members will need time to understand how it affects their own personal position. The crude and unfair manner in which ministers have tried to impose their will on staff has provoked huge concerns which could all too easily prompt many to opt out of the scheme or exit the service altogether.

"That is why we will continue to campaign against the imposition of higher contributions in April, on top of a third year of pay curbs and the unrelenting pace of job cuts."