Of 875 ballot papers issued to eligible members of the energy union, 622 voted – 590 saying yes and only 32 saying no to action.

Members of two other unions – Unite and Unison – also voted strongly in favour of action, if the company does not come back with an improved offer.

Prospect National Secretary Emily Boase said that the three unions have fixed fresh talks with the company.

“This result shows the strength of feeling among members. They are dedicated and often go beyond the call of duty to ensure a service to the public and commercial customers. They would not have voted for industrial action without very good reason. They accepted 1.3% last year but they can’t afford to do it again.

“We urge National Grid to see sense and hand back some of their profits to their hard-working, loyal workforce. The company’s 12% increase in pre-tax profits and 8% increase in dividends are down to the efforts of the workforce, whose contribution deserves to be recognised.”

If talks fail, any action would start later this month, but members would respond to emergencies and ensure vulnerable people are not affected.The unions claimed a one-year increase linked to RPI inflation – 5.1% on the review date. But National Grid offered 2.5% from July 1 this year; 2.25% from July 1, 2011; and 2.25% from July 1, 2012. The offer is also conditional on unions agreeing to a review of the performance bonus system.

Prospect has 1,050 members in National Grid, including grid systems engineers, field engineers, gas operations engineers, office-based development engineers and managers working with new connections. Personal contract holders were not balloted.