British Gas engineers make three million breakdown visits a year

The GMB union said nearly 6,000 engineers, who repair and service domestic boilers, backed the move by a ratio of four to one.

Strike dates will be set next week, and are likely to start over Christmas, the union said.

Meanwhile, the company said it was confident it could cover emergencies during any industrial action.

The engineers are angry at parent company Centrica's plans to close their final salary pension scheme for new entrants from January.

Brian Strutton, the GMB's national secretary, said: "They are determined to protect their pension and the pension of future British Gas engineers.

"They had exactly the same agreement two years ago when British Gas/Centrica and its engineers reached a deal to increase their contributions, which the company is now breaking."

Pensions challenge

British Gas said the strike action was unwarranted as none of the engineers would be affected by changes to the pension scheme.

"The pensions package for new employees is recognised by independent financial experts as one of the best in the market," said David Kendle, director of British Gas Services.