A bitter dispute over the use of foreign workers on a multimillion-pound construction project at an oil refinery spread across the country after a series of wildcat strikes were called.
A decision to bring in hundreds of Italian and Portuguese contractors to work on a new £200 million plant at the giant Lindsey Oil Refinery in north Lincolnshire, led to protests in support of jobs for British workers.
Several hundred demonstrators gathered for a third day outside the plant following a walk-out by contractors on Wednesday, but the unofficial action spread to other parts of the UK, including Scotland and Wales.
Hundreds of workers at the giant Grangemouth oil refinery in Scotland walked out following an early morning meeting.
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The mechanical contractors, who work for BP and INEOS, said they were supporting their colleagues in Lincolnshire.
Bobby Buirds, a regional officer for the union Unite in Scotland, said the workers at Grangemouth were striking to protect British jobs.