A bitter dispute over the use of foreign workers on a multimillion-pound construction project spread to several other sites today when police were called to a series of wildcat strikes.

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 at North Killingholme, 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.

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.

"The argument is not against foreign workers, it's against foreign companies discriminating against British labour.

"If the job of these mechanical contractors at INEOS finishes and they try and get jobs down south, the jobs are already occupied by foreign labour and their opportunities are decreasing.

"This is a fight for work. It is a fight for the right to work in our own country. It is not a racist argument at all."

Unions will hold another meeting of Scottish shop stewards in Glasgow this afternoon, and a further meeting on Monday, he said.

Police were called to the Aberthaw power station near Barry in South Wales after workers staged a protest.

Around 400 workers staged a demonstration at the Wilton refinery in Teesside. Cleveland Police said the workers were picketing the site near Redcar, adding: "The protest started at around 6.30am with 400 workers taking part.

"They are picketing four gates around the refinery. The protest is peaceful and officers are monitoring the situation."

The refinery dispute erupted after Total put the Lincolnshire contract to build the new unit, which will allow the refinery to process crude oil with a higher sulphur content, out to tender.

Five UK firms and two European contractors tendered for the work and it was awarded to the Italian company Irem on the basis that it was supplying its own permanent workforce.

It is understood 100 Italian and Portuguese workers are on the site. They are expected to be joined by 300 more next month. The foreign workers are accommodated in large, grey housing barges which are moored in Grimsby docks.

Cleethorpes MP Shona McIsaac said the decision was "like a red rag to a bull for people in our community who are out of work and who have skills that could be used in this construction project".

But Total said the Irem contract involved no anticipated redundancies from the existing contractor workforce and stressed that local companies would be providing additional support services to the project.

The firm also said Irem staff would be paid at the UK nationally-agreed levels for the engineering construction industry under the same terms and conditions as agreed with unions for the existing contractor workforce.

Derek Simpson, joint leader of Unite, called for urgent meetings with the Government and employers to discuss the "exclusion" of UK workers from some of Britain's major engineering and construction projects.

Several hundred protesters gathered in a car park opposite the sprawling oil refinery in Lincolnshire, many holding placards and banners expressing their anger.

One placard said "Right to Work UK Workers", while another read "In the wise words of Gordon Brown UK Jobs for British Workers".

Unite said mechanical contractors at six other Scottish sites, in addition to Grangemouth, were also taking industrial action.

Around 500 walked out at Scottish Power's Longannet power station, and just over 100 at its Cockenzie power station, while around 80 stopped work at British Energy's Torness facility.

At the Shell St Fergus gas processing facility in Aberdeenshire, around 50 workers downed tools, while about 100 stopped work at ExxonMobil's petrochemicals plant at Mossmoran in Fife and some workers at the Shell plant at Mossmoran have also stopped work.

There was no demonstration at Grangemouth today and a spokesman for INEOS said the industrial action was not affecting operations or safety.

He said: "We are very disappointed that the contractors have chosen to walk out, especially as we've got a good working relationship with them.

"Our plants are operational and there is no issue as regards safety, and there will be no impact on production levels at all."

He said not all the contractors at Grangemouth are covered by the National Joint Council for the Engineering Construction Industry (NAECI) agreement, which agrees common terms and conditions for contractors across the UK, and some were still working as normal.

The Grangemouth walk-out included around 100 workers with contractors employed by BP, the oil giant said.

They work at the Kinneil terminal - part of the Grangemouth complex where North Sea oil from the Forties pipeline system comes ashore.

A BP spokesman said: "The workers are not involved in day-to-day operations and the Forties pipeline system will continue to operate as normal."

The Grangemouth refinery was sold by BP to INEOS in 2005.

A spokeswoman for RWE npower, which runs the Aberthaw power station, said about 50 contract workers were "peacefully" demonstrating at the entrance to the site.

She said: "Police are on site and have sectioned off an area for the demonstration.

"No RWE npower staff are involved and Aberthaw power station continues to operate normally.

"We understand that the demonstration reflects other activities supporting action at the Lindsey Oil Refinery at North Killingholme."

A South Wales Police spokeswoman said: "Our first priority is the safety of the public and the protesters at the site.

"We are in communication with the protesters and are facilitating a lawful protest."