A strike could halt production at Britain’s biggest chocolate company after workers overwhelmingly rejected Cadbury’s plans to close a factory and shift production of brands such as Curly Wurly and Fudge to Poland.

In the latest blow to the British chocolate industry, Cadbury plans to close the historic former Fry’s Somerdale factory at Kenysham, near Bristol. The move will result in the loss of 500 jobs and transfer of some of the production to the company’s Bournville plant in Birmingham. Even there, a further 200 jobs will be lost.

By 2010, a new plant in Poland is intended to produce some if not most of the brands made at Keynsham, including Curly Wurly, Fudge, Turkish Delight, Fry’s Chocolate Cream and Cadbury’s Mini-Egg.

In a ballot announced yesterday, workers at all four of Cadbury’s chocolate-making plants in the UK – Keynsham, Bournville, Marlbrook in Herefordshire and Chirk in north Wales – rejected the plan by 1,363 to 130, a majority of 9-1. A call for a ballot on industrial action was backed by 1,090 to 312. Union leaders and managers will be locked in talks for the next few weeks to discuss whether to go ahead with the move. It is also opposed by the Labour MP for Wansdyke, in Somerset, Dan Norris.

Cadbury says the redundancies are necessary to cut costs. It points out that it is spending £40m on turning its plant at Bournville into the world’s most sophisticated chocolate factory.

Unite, the country’s biggest union, says the move was financially unnecessary for a company with worldwide annual sales of £3bn, and, environmentally, would add millions of food miles to its products. “The result of this ballot reflects the anger that emanated from Somerdale to the other sites – the proposals have unsettled the workforce,” said Steve Preddy, the regional organiser for Unite.

Cadbury’s spokesman, Tony Bilsborough, said the ballot was “not a vote for industrial action” and said the company would continue to consult with unions over the redundancies, which it hopes will be voluntary.

By shifting production abroad, Cadbury, which has 30 per cent of UK sales, is following in the footsteps of smaller rivals in the British confectionery market – Mars, Nestlé and Kraft. Two years ago Mars, with 20 per cent of the UK market, announced the closure of a factory in Slough with the loss of 500 jobs and transferred production of Twix bars to France and Germany, and Starburst sweets to the Czech Republic. A further 200 jobs were lost at five plants in Leicestershire, Peterborough, King’s Lynn and Leeds.

In the same year, Kraft closed its Terry’s chocolate plant in York, ending a century of chocolate-making in the city, with the loss of 316 staff; Terry’s All Gold and Chocolate Oranges are now made in Sweden, Poland and Slovakia.

Last year, Nestlé announced the loss of 645 jobs from its factory in York, with production of Smarties moving to Germany, Black Magic to the Czech Republic, and Dairy Box to Spain.

Unite claims the job losses are a panic response to Cadbury’s failure, announced last month, to find a buyer for its 7-Up and Dr Pepper drinks business.

A Unite spokesman, Andrew Dodgson, blamed “corporate greed” for the decision, which he warned might not make sense in the medium term because the exodus of workers from Poland was raising labour costs there.