STRIKE action at dump truck factory Caterpillar could be set to escalate.

Workers at the Peterlee, County Durham, factory were due to continue their series of one-day strikes today.

But, Davey Hall, regional convenor for the AEEU/Amicus, warned that the action may escalate if no agreement on pay was reached.

Workers have been picketing the plant every Tuesday in a bid to overturn a three-year pay freeze.

Caterpillar management has offered to reduce the pay freeze to two years, an issue that the workers were being balloted on last night.

Mr Hall said the deal was put to a mass meeting on Saturday. "It was explained to them that if they voted yes to the new deal, then the strike action would end. However, if they vote no to the deal, then there will be all-out action from Monday, February 18."

The dispute at Caterpillar is part of growing industrial unrest. Yesterday, benefit office workers across the UK took action over the removal of security screens in their offices, while South West Trains only managed to run a third of trains after the RMT union took industrial action.

And Metro operator Nexus faces a series of one-day strikes as workers demand better pay. The 76 members of Nexus' 1,000-strong workforce belonging to train drivers' union Aslef voted for industrial action after rejecting a three per cent pay offer.

The Government claimed yesterday's strikes at job centres had not been fully supported by staff. Work and Pensions Secretary Alistair Darling said the vast majority of staff in JobCentre Plus offices had stayed at work.

Meanwhile, medical secretaries in the City of Sunderland Hospitals NHS Trust and Northumbria Healthcare Trust are to be balloted by Unison on strike action over pay. The ballot is due to take place on Monday.

Yesterday, South West Trains brought in managers to take the place of guards and other staff and said it would carry on replacing striking workers until industrial action was "irrelevant".

The firm was able to run 600 out of a usual 1,700 trains across the South-East and into London's Waterloo station, and laid on more than 100 buses and coaches to replace cancelled services.

Meanwhile, the RMT has praised the commitment and resolve of its conductor members in dispute with Arriva Trains Northern for holding "absolutely firm" during last week's strike action.

The union said none of its members went to work on the strike days, resulting in 90 per cent of services being cancelled.