Britain's biggest public-sector union, Unison, one of more than a dozen unions locked in a row with the government over pension reform, said on Thursday its members had voted in favour of a national strike later this month, piling pressure on ministers.

Announcing the result of a strike ballot involving a record 1.1 million workers, Unison said its members had given overwhelming support for a 24-hour strike on November 30.

It said 245,000 had voted in favour and 70,000 voted against a strike.

The result, on a turnout of 29 percent, comes a day after a coalition of unions involved in the dispute said they were pressing ahead with plans for a strike despite a new offer on pensions that ministers describe as the chance of a lifetime.

General Secretary Dave Prentis said: The decisive 'yes' vote in the ballot reflects the deep concern that our members have over government ministers' proposals for their pensions.

He said the union supported the stoppage but will be negotiating right up to then and beyond to get a fair deal for our members.

Unions are balloting members on industrial action over changes to their pensions and are due to report results in the coming weeks, raising the prospect of the biggest British strike in decades.

Unison, which represents staff in public services ranging from health workers to refuse collectors and social workers, said it would now consider what steps to take and would announce a decision later on Thursday.

The government has said it will scrutinise details of how many workers took part in the ballot as well as any majority in favour of action.

(Reporting by Stefano Ambrogi; Editing by Steve Addison)