Unions have hailed a strike by up to two million public sector workers as “historic” as they angrily rejected claims by the Prime Minister that the biggest walk-out in a generation had been a “damp squib”.

David Cameron told the Commons that the “irresponsible and damaging” industrial action had been far from universally supported as he defended the Government’s controversial pension reforms.

Officials from 30 unions involved in the strike reported huge support, with up to 90 per cent of some organisations taking action, often for the first time in their lives.

The strike closed more than three-quarters of schools in England, as well as courts, museums, libraries and jobcentres, disrupted transport, hospitals and government departments, led to around 15 per cent of driving tests being cancelled and was described by unions as the biggest since the 1979 Winter of Discontent.

Civil service union Prospect said action by 26,000 of its members alone disrupted or stopped work at more than 400 locations, ranging from Ministry of Defence sites to prisons, while more than 1,000 rallies were held across the UK.

Len McCluskey, leader of Unite, said the rallies showed the depth of anger among public-sector workers, adding: “The Government can try to spin and tell lies, but they have been found out.”

Unison leader Dave Prentis said: “I wouldn’t call two million people taking strike action a damp squib.

“Cameron is sounding increasingly desperate in his attacks on public service workers.”