Airports in the U.K. were spared from gridlock and pandemonium on Wednesday when two million workers went on strike to protest the increase in retirement age.

Air travelers did not suffer from long queues and delays in passport clearance expected at London's Heathrow and Gatwick airportd due to striking immigration officers.

Colin Matthews, CEO of BAA, which operates Heathrow, said "pandemonium" had been averted through careful planning, according to Atwonline.com.

Airport officials had asked airlines to reduce their passenger load by half days before strike. Airlines rebooked Wednesday flights for free while others cancelled flights to London for that day.

The U.K. Border Agency also deployed replacement staff trained months before the strike.

The strike closed some 20,000 schools nationwide, postponed 7,000 scheduled surgeries in hospitals and crippled transportation in Northern Ireland.

About 1.09 million state workers in England, Wales and Scotland joined the strike.

Police arrested 21 Occupy London protesters for trespassing and burglary after they went inside a building housing the office of mining company Xstrata in London's Panton Street.