A planned strike by workers at a giant oil refinery will lead to fuel shortages from next Friday and could cripple supplies for a month, its owners have warned.

Up to 1,200 workers at the Grangemouth site in Scotland will walk out on April 27 and 28 in a row over pensions.

The site's owner, Ineos, said that the industrial action could mean no fuel supplies in Scotland and the North of England for at least a month, although the Unite union has warned that the whole of the UK would be hit.

Ineos said it had been left with no option but to begin shutting down the site - Scotland's only crude oil refinery - immediately. And the company warned that fuel shortages were likely to start as early as next Friday.

Ineos said it had decided on safety grounds to start shutting down Grangemouth because it wanted the site to be safe during the strike period.

The firm said the measures were being forced on it because of the strike, which has been called in protest at plans to close the final salary pension scheme to new workers as well as other changes.

Ineos said it had made concessions to Unite and guaranteed that no changes would be made to existing pensions before next April, and accused the union of "rushing" to take industrial action.

The company said the stoppage would also effectively close down a large proportion of North Sea oil production as well as some gas production which goes through Grangemouth.

Chief executive Tom Crotty said: "This is a huge oil refinery and they (the union) know you can't just turn it on and off like a tap. A month is our best guess but safety considerations will be at the forefront of everything we do."

He warned that the strike threatened the investment as well as hundreds of jobs and would damage the UK economy.