The government has been accused of using “misleading data” in a bid to “manipulate” opinion over its controversial reform of public sector pensions, which is set to spark the biggest strike in decades.

Unite said chief secretary to the Treasury Danny Alexander had used “distorted” figures during speeches last week and in an official Treasury document entitled Public Sector Pensions: Good Pensions That Last.

Mr Alexander gave the example of a nurse retiring on a salary of £34,200, saying he or she would receive a pension of £22,800 a year under the scheme being proposed by the government.

Unite said an analysis by its pension experts found that this example was based on a comparison of a nurse working for 43 years and retiring at 68 in the proposed scheme rather than working for 35 years and retiring at 60 under the current arrangements.

The pension quoted by the government involved working and contributing for eight years more and receiving the pension for eight years less, said Unite.

Unite also questioned the minister’s pledge that public sector workers will not have their retirement income affected if they are due to retire in the next 10 years, saying the change to linking pension rises from RPI to CPI inflation alone will reduce pensions.

Assistant general secretary Gail Cartmail said: “He’s using distorted figures to conceal the way in which government proposals will reduce pensions. Most NHS workers will not get a pension anywhere near this maximum full-time service example, and many will have lower pay than the qualified nurse he has focused on, but all will suffer similar proportionate losses to those he is trying to conceal. Currently the average (median) pension received by NHS workers is only around £4,087.”

The TUC has called a day of action on November 30 against the pension reforms, which could involve over two million workers going on strike, the biggest number since the 1979 Winter of Discontent.

Unison, the biggest public sector union, announced last week that its members had voted to take industrial action, and several more unions, representing council workers, teachers, civil servants and health staff, will disclose their ballot results in the next two weeks.

A Treasury spokesman said: “As many objective observers have noted, we have made a generous offer and set this out in unambiguous terms.

“Public service workers can judge this offer for themselves by visiting www.hm-treasury.gov.uk.”