An outline agreement has been reached covering health workers' pensions, British union sources said on Monday, in a sign a broader breakthrough could be imminent in a bitter dispute with the government over public sector pension reform.

The heated row drew hundreds of thousands of workers out on strike last month in the biggest national walkout for decades and unions have threatened more stoppages next year.

A union source said an agreement in principle had been hammered out with government officials covering at least 450,000 workers in the health sector, with talks continuing across three others: teaching, local government, and the civil service.

A 'heads of agreement' has indeed been reached (on health)...similarly we're expecting the same in local government and hopefully some progress in the civil service scheme as well, but teacher talks are ongoing, Brian Strutton, national secretary for the GMB, the third largest union involved in the talks, told Reuters.

Strutton said the deal for health workers was encouraging but that it still needed to be approved by union executives at meetings in the New Year.

It's a major step forward in negotiations because a large part of the parameters have been agreed in principle subject to final application by members...but no one should underestimate the difficulties of finishing off the detail and then getting it approved by health workers out there, he said.

However, it takes us forward in negotiations and that means government won't impose any change while they continue talking and we won't call any further industrial action (in terms of health), Strutton added.

He said lifting the threat of industrial action may extend to other sectors as well if deals are struck in other sectors.

On some issues, such as contribution rates for the low-paid next year, and for people close to retirement, we have made progress, said Christina McAnea, Unison's head of health said in response to the government's offer

We've gone through the gateway the government asked us to do by the end of the year, to reach heads of agreement on the main items, and that carries the detail negotiations through into next year, another union source close to the talks said.

There's still a bit to be done it's not over yet

The government said it remained hopeful of a deal on pensions involving all of the schemes by the end of the year.

The Chief Secretary to the Treasury, Danny Alexander, will make a statement on progress in the negotiations to parliament on Tuesday.

(Reporting by Stefano Ambrogi; editing by Keith Weir)