Business leaders have pledged their support to staff at two Norwich factories following announcements that both may close.

Soft drinks giant Britvic revealed today that it is planning to close its manufacturing base in the city, impacting 242 jobs.

This was closely followed by an announcement from the maker of Colman's mustard Unilever, which shares the site on Bracondale, that it was considering the future of its own factory, where 113 people are employed.

Stefan Gurney, executive director of Norwich Business Improvement District (BID), said any loss of manufacturing business in the city would be a blow to the local economy and community.

'We want the city to retain a business of manufacturing. Both companies have long links with the city, so we would be sad to see the closure of those businesses, especially considering that if Unilever left there would be no production of Colman's Mustard in the city. That is such an iconic Norwich brand and so historically linked with the city.

'We do not want to see anything that loses jobs and revenue for the city. Britvic going is a lost opportunity, but there is also the knock-on impact on how viable the site remains for Unilever. Britvic's decision is not impacting solely themselves, it is impacting the whole site.

'It is a big concern and we will be speaking with the Norfolk Chamber of Commerce and both local authorities to see what conversations we can have with Unilever to work out a process to ensure we have Colman's manufactured in or still part of the heritage of the city.'

Chloe Smith, MP for Norwich North, said: 'This is very sad news and many constituents will be very anxious about this possible closure. At this stage, I am urging the company to make every support available to those workers.'

The GMB union, which has 150 members at the Britvic site, said it was 'very concerned' at the plans.

Ivan Mercer, GMB regional organiser, said: 'This is not just a blow for Norwich but Norfolk manufacturing in general as employees live across the whole of the county.

'GMB will do everything we can to mitigate the effects of closure on our members and will seek to meet with the company at the earliest opportunity to discuss this proposal further.'

The New Anglia Local Enterprise Partnership has said it would be contacting both companies to find out about their plans, and would support workers where possible.

Chris Starkie, managing director, said: 'We will be writing to both companies to understand their plans in more detail and to see if there is any possibility the decision at Britvic could be reversed and to urge Unilever to keep open its Colman's factory.

'We will also be working with our local authority partners to provide support for those employees affected by the decision, in terms of retraining and opportunities for other jobs.'

Mr Starkie added: 'While this is a sad day for companies with a proud history in Norwich, the food and drink industry in Norfolk and Suffolk is strong. With three new Food Enterprise Zones across the East and a number of other companies expanding and continuing to grow, we hope and expect there to be fresh opportunities for employment in the future.'

Alan Waters, leader of Norwich City Council, said the authority was 'very shocked' to hear about the 'large number of jobs at risk'. 'Well-paid and skilled manufacturing jobs – and the supply chains they support – are vital to Norwich's economy,' he said.

'We are also deeply concerned about the knock-on effects this could have for the iconic and internationally renowned brand of Colman's.

'I have asked for an urgent meeting with Unilever and Britvic to discuss the matter and also find out how we can work together with parties such as the Local Enterprise Partnership to see if we can safeguard existing jobs and operations.'

Nova Fairbank, public affairs manager for Norfolk Chamber of Commerce, said: 'Colman's Mustard has been produced at the same factory in Norwich since the 1860s and in 1896, J.J. Colman became the first president of Norfolk Chamber of Commerce.

'In view of their long history with our region, the number of local jobs dependent on them, and that they are one of the last original iconic Norfolk brands, we would strongly encourage the Colman's to remain in Norwich.'