Thousands of British doctors took industrial action today for the first time in nearly 40 years, in a row over changes to their pensions as part of government austerity measures.

The British Medical Association (BMA) union said doctors were boycotting routine hospital appointments and non-emergency operations for 24 hours but emergency care was not affected.

The BMA said the government is reneging on a 2008 deal, and says plans to make doctors work until they are 68 years old and pay more towards their pensions are "totally unjustified".

"Nobody likes taking anything that will inconvenience patients and I know a lot of doctors who have taken this step very unwillingly," BMA chairman Hamish Meldrum said as the first doctors' strike since 1975 got under way.

Prime Minister David Cameron's government, which is battling a vast black hole in its public sector pensions budget, says rising life expectancy means the current scheme is unsustainable.

The new scheme will still be generous, it adds, with a doctor who starts work in 2015 receiving pension payments of around £68,000 ($106,800, 84,300 euros) a year in current prices if they worked until they were 68 years old.

Health minister Andrew Lansley, whose government has introduced steep austerity measures in a bid to shrink its yawning deficit, said the strike could result in the cancellation of up to 30,000 operations.

"I can't see why anybody thinks there is any benefit in penalising patients," he told ITV.

Participation in the strike varied across Britain, with the BMA estimating that four out of five hospitals would have to cancel some procedures, while one in three family doctors were taking part.

With more than 100,000 members, the BMA represents around two thirds of Britain's doctors. Eight out of 10 voted to strike, on a turnout of 50 percent.