The fall-out from the closure of Norwich's Colman's and Britvic factories could ultimately cost 1,000 jobs and £10m in lost wages, the union which has been fighting the plans has claimed.

The GMB says that the impact of the withdrawal from Carrow Works will go far beyond the 355 workers at the two factories, spreading through the supply chain in the county and drawing well-paid jobs away from Norfolk.

The union was responding to confirmation that the first phase of consultation at Colman's owner Unilever had drawn to a close, with the company confirming it would follow Britvic in leaving the site by 2019.

As a result, 113 posts are at risk, with 43 members of staff expected to relocate to Unilever's production site in Burton. The company has said a new mustard-milling facility in the city will create around 25 jobs, but has offered little detail on the plans.

Ivan Mercer, GMB regional officer, said confirmation of the closure was 'simply devastating for the workers, and wider Norwich community'.

'No one believes the company's claim that a small consortium of local farmers are maintaining the Colman's legacy of production, that is just marketing spin.

'It is worth noting that the company have been represented in meetings with local authorities by communications directors and managers.

'But for the Norwich community the combined closure of both Britvic/Robinsons and Colman's will result in nearly 1,000 direct and indirect job losses, and nearly £10 million of wages sucked out of the local economy.'

He said members felt the decision had been 'predetermined', and that the 'company have been prepared to sacrifice the Colman's legacy purely for greater margins'.

READ MORE: 'Very sad... Unilever will be judged by generosity of support to staff' – Sir Timothy Colman on Norwich factory closureNorwich City Council leader Alan Waters said the authority had been working alongside the unions, county council, New Anglia LEP and city MPs Chloe Smith and Clive Lewis to find a new site for Unilever in the city.

He added: 'This is a disappointing outcome from the Unilever review process and a blow to the local economy. We will continue to work proactively with both companies to assist the workforce and their families through these difficult times. In reality, the council has very little influence to change the decision of either company during Unilever's review process.'

The GMB is also seeking an urgent meeting with business secretary Greg Clark to explore alternative proposals.