Cabinet ministers have been quietly approving hefty pay rises for some of their own special advisers while freezing or imposing sub-inflation increases on the pay of millions of other civil servants and public sector workers, official figures show.

The rises – which in the case of one special adviser at Iain Duncan Smith's Department for Work and Pensions was 36% last year – were condemned as outrageous last night by civil service unions and the Labour party.

The news follows a decision last week by Jeremy Hunt to refuse an across-the-board pay rise to hundreds of thousands of NHS staff.

This increase had been recommended by an official pay review board, and the decision means that NHS workers and many others in the public sector will now face a fourth year of below-inflation rises.

The same tough settlements have not applied, however, to several ministerial special advisers ("spads"), who are temporary civil servants employed to give political advice to ministers.

Last year David Cameron's own chief of staff, Ed Llewellyn, received a 12% increase, from £125,000 to £140,000, which means he now earns more than double the £66,396 salary of an MP.

Philippa Stroud, a special adviser to Duncan Smith, saw her pay increase last year by even more: a 36% rise from £69,250 to £94,000 last year.

Fiona Cunningham and Nick Timothy, two special advisers to the home secretary, Theresa May, were bumped up last year by 14% from £65,000 to £74,000 while several others had smaller above-inflation increases.

A spokesman for the Cabinet Office said that any pay increases would have to have been approved by a special committee – chaired by the chief secretary to the Treasury, Danny Alexander – that deals with special advisers' remuneration. The coalition promised to clamp down on the number of special advisers who are temporary civil servants, but the bill for them has risen, as have their numbers, since 2010.

Chi Onwurah MP, shadow cabinet office minister, said: "The government has singled out nurses and thousands of other health workers not to receive a 1% pay rise, but at the same time ministers are happy to sign off on massive wage increases for their political advisers.

"David Cameron has already broken his promise to limit the number of special advisers, and now many of them are getting bumper pay rises. It beggars belief."

Marc Serwotka, general secretary of the Public and Commercial Services Union, which represents around 250,000 rank-and-file civil servants, said: "The fact that low-paid civil servants have had their wages cut for successive years while political advisers are getting pay rises tells us everything that we need to know about this government and its priorities. It's an absolute disgrace."