Several hundred contract workers at power stations across the U.K. downed tools Friday or continued unofficial strike action in support of workers at oil major Total SA's (TOT) Lindsey oil refinery in northern England, utility companies and contractors said.

However, no staff from the utility companies were involved in the strikes and operations at all the sites was unaffected, the companies said.

Over 400 contract workers at three of RWE AG's (RWE.XE) U.K. power stations walked out Friday, the German utility's U.K. unit RWE npower said.

Around 300 contractors, who work on either construction or maintenance projects at RWE npower's Aberthaw power station in Wales and around 60 contractors working on maintenance at Didcot A power plant in southeast England walked out earlier Friday, the company said in an emailed statement.

A spokeswoman for contractor Alstom said between 60 to 90 scaffolders were in the second day of a walkout at RWE npower's Staythorpe power station in northern England.

A number of workers at British Energy's Hinkley Point B nuclear power station also walked out Friday morning, but operations at the site are continuing as normal, according to a spokeswoman for British Energy, the U.K. nuclear unit of France's Electricite de France SA (EDF.FR).

Around 150 contractors for routine maintenance work at E.ON AG's (EOAN.XE) Ratcliffe power plant in northeast England are out for a second day following a walkout Thursday, said a spokeswoman from the company's U.K. subsidiary E.ON U.K.

Meanwhile, contractors from EDF Energy's Cottam plant in northeast England have returned to work, a spokeswoman said.

Contractor Doosan Babcock said in a statement a "small number" of its employees are participating in unofficial action at a small number of sites where it operates. Doosan Babcock didn't name the sites or say how many contract workers were involved.

Earlier Friday, Total said it had terminated the contracts of 647 contract workers at the Lindsey refinery following unofficial strike action.

The strikes started at the 200,000 barrels-a-day refinery last week following a dispute with a subcontractor over 51 layoffs.

-By Selina Williams, Dow Jones Newswires +44 207 842 9262; selina.williams@dowjones.com