A unique and detailed analysis has revealed which sectors of the economy would suffer most from a radical reduction in EU migration to Britain.

According to a GMB study of figures produced by the Office for National Statistics, in at least 18 specialist industries EU workers constitute more than 20% of the labour force. And many others would be left almost as bereft if their number declined.

The government insists EU workers living here will be able to stay post-Brexit. But there are fears that many will choose to leave when the drawbridge is raised in 2019 and that an eventual end of free movement will see future vacancies left unfilled.

Last week it was announced that the independent Migration Advisory Committee will examine the economic and social contributions and costs of EU citizens in Britain. Concerns over the impact on the NHS and residential care have been highlighted in recent months. But the ONS study reveals a reliance on EU workers across a broad range of industries, extending far beyond the caring professions.

It shows that nearly half – 47.6% – of employees in the fruit and vegetable “processing and preserving sector” are from EU countries. A similar proportion – 44.4% – are involved in meat processing. More than a third – 37.6% – of those processing fish, crustaceans and molluscs are EU migrants.

In agriculture, just under 35% of workers employed in what the ONS describes as the “growing of nonperennial crops” are EU citizens, along with more than a quarter of workers involved in the manufacture of prepared animal feed. And just under a quarter involved in the “manufacture of bakery & farinaceous [starch] products” are EU workers.

Many specialist sectors heavily reliant on people from other EU countries employ only a few thousand workers. Just over 1,000 EU nationals are employed in “the cutting, shaping and finishing stone industries”. But they constitute 22% of the workforce.

Outside of manufacturing, entire industries rely on EU workers for a sizeable portion of their labour force. They make up almost 230,000 of the 1.7 million people working in the hotel and catering industry – 13.5% of the total.

“Manufacturing is a real money-spinner for the economy,” said Jude Brimble, national secretary for manufacturing at the GMB union. “It provides good jobs and stimulates the supply chain in local communities, and, as these figures show, the whole sector is heavily reliant on the work of EU nationals. Workers from both the EU and the UK, as well as companies themselves, are understandably worried about what lies ahead.”

EU nationals comprise almost a third – 32% – of the 24,000 people employed in translation services. Roy Allkin, chair of the Association of Translation Companies, said the industry was worth £1.2bn to the UK. “At the moment the UK is a hub for internationalisation and language services because of how free we have been in the movement of people and things like that, and because people trust us as a business centre.

“If those advantages are taken away from us, where is that business going to go? At my own company, Wolfestone, we have about 35 employees, and I would say that probably at least 40 to 45% of the employees are from the EU. If free movement is restricted, that could hit us massively.”

Amid concerns from business about the impact that Brexit will have on the labour market, the home secretary, Amber Rudd, has said that the government would be seeking a transitional arrangement, which may involve the continuation of free movement, to ensure there would be no “cliff edge” for employers.

Brimble said: “If the government want to avoid driving the economy off a cliff, they need to engage with business and unions to make sure EU nationals who are already working in crucial roles, contributing to our economy, are protected, and to ensure proper workforce and skills planning for the future.”

Jimmy Buchan, business manager at the Scottish Seafood Association, which is likely to be affected by any shortage of EU workers, said some industries may need special dispensation if Brexit looked like it would cause a labour shortage.

“The ideal situation would be that they get to remain here,” said Buchan, who is supportive of Brexit because it will allow the fishing industry “to take control” of UK waters. “But look, we couldn’t have an open border. There comes a point in time where we run out of space, so there’ll have to be a controlled measure. So it’s how that controlled measure is implemented. If there is a clear need for a sector to have a free flow of people, then it should be granted, but on a case-by-case study of what the sector needs.”