Union leaders have warned Jaguar workers that they risk allowing the Castle Bromwich factory to "wither and die on the vine" if they do not agree to new working practices.

In a hard-hitting brief to the shopfloor, Unite union warned that new models could go to the likes of China and Brazil unless revised efficiency plans are voted through.

The warning was issued to Jaguar workers 24 hours ahead of tomorrow’s crucial ballot on a range of new practices, including compulsory Saturday working. In May initial plans were rejected by 1,153 against to 756 votes in favour.

The Unite briefing document, which is unanimously recommended for acceptance by union leaders and local MP Jack Dromey, says: "We all know the company are now considering making significant massive investment into Castle Bromwich with new facilities and importantly, further several new models.

"However, we recognise the danger that this is not cut and dried. Investment in new plant and important crucial further models could just as easily go elsewhere in the UK or even abroad such as China or Brazil.

"None of us want to see our plant wither and die on the vine for lack of a secure long-term future.

"This chance for Castle Bromwich is our best opportunity in a decade to secure the long-term future of the plant. After all our years of hard fighting we can’t afford to let it slip through our fingers now."

Erdington MP Jack Dromey, who helped drive the campaign to save the Castle Bromwich factory from closure two years ago, said: "We now have the best chance we will ever have to guarantee a growing Jag for decades to come. The company must play its part.

"So too must the Government. But so too must the workers. If we get it right, billions more will be invested in new product. 1,000 more Jag jobs, new apprenticeships and workers able to get on, earning more money.

"I know from my experience of 30 years of fighting for workers that you sometimes get a once in a generation opportunity. This is it. I hope the workforce back their union."