More than 1,200 workers forced to down tools this weekend at the Cowley Mini plant due to the Spanish fuel crisis could each be £120 out of pocket, the Oxford Mail can reveal.

While bosses have confirmed production line staff will be paid their basic wage, it does not include the 31 per cent premium those on the weekend shift normally receive.

As a result, they will not only have to work the lost hours, but also claw back the weekend premium. Union convenor Bernard Moss said: "The biggest effect is on the weekend shift. If they don't work, they lose almost a third of their money."

A total of 4,000 staff across four shifts could be affected by the enforced lay-off caused by striking Spanish truck drivers, which has meant brake discs could not be delivered to the plant.

Work is not due to start again until Monday night. Mr Moss said under terms and conditions negotiated when BMW took over the plant from Rover in 1999, hours must be given back under the company's working time agreement.

He added: "This is just being treated as a lay-off. It does not matter whether the plant is on strike or there is a problem with the supply chain."

Bosses said opportunities to make up the time have been arranged with planned production breaks at the factory in June and July called off.

Plant spokesman Rebecca Baxter said: "Agreements were originally made with the full co-operation of the trade unions and membership with the whole point being to stabilise income.

"This is something beyond our control and the situation will even out with working through the production breaks."

Ms Baxter added: "We operate a flexible shift pattern and can turn production up in response to demand."

The strike by Spanish hauliers, who are protesting over soaring fuel prices, has blocked roads and hit exports.