Public sector workers will have to produce a medical certificate after five days off sick if they don't want their pay docked, it has been announced.

A report from a ministerial task force chaired by Alan Johnson, the work and pensions secretary, also suggests that workers who take more than five separate absences in a year should be given a disciplinary warning.

Public sector workers take an average 10 days per year off sick, compared with 7.8 days in the private sector.

Mark Serwotka, general secretary of the Public and Commercial Services Union, said: "We have always argued that if you are serious about tackling sick absence you need to look at the real causes and deal with them in a positive manner. Stress is a major factor of ill health in the civil service."

The announcement came alongside new plans to overhaul civil service pensions.

Under the Cabinet Office rethink the retirement age will rise from 60 to 65 and payments will be on a "career average" rather than final salary basis.

Unions have not ruled out strike action over the move.