The number of EU migrants applying to work in rural Suffolk has dropped by 22% since the Brexit referendum – prompting concern from the biggest farmers’ union in East Anglia.

The statistics, from the Department for Work and Pensions, show how many foreign nationals have successfully applied for National Insurance numbers, which are required to work or claim benefits.

The data shows that fewer EU citizens are applying for NI numbers across the board – comparing the number who applied to work in the year prior to the referendum with those seeking NI numbers between March 2017 and 2018.

A total of 2,528 people from the EU applied to work in rural Suffolk in the year leading up to the Brexit vote, compared to 1,983 in 2017/18 – a drop of 545 people (22%) in just two years.

Many EU migrants come to Suffolk to do seasonal work – often taking up agricultural jobs on farms, ranging from harvesting to fruit picking.

In Forest Heath, there has been a 26% dip in EU citizens applying to work, while in Waveney the percentage drop rises to 31%, and in Babergh there has been a 35% reduction in migrants applying for NI numbers – a decrease of more than a third in just two years.

In St Edmundsbury, the percentage drop is 20%, while the difference is much lower in Suffolk Coastal, at 7%.

There has been concern that there will be a workforce gap after Brexit, particularly in catering, construction and agriculture – which the justice secretary David Gauke has said could be filled by prisoners.

Representing farmers across the region, the NFU said: “Securing access to a reliable and competent labour force after Brexit is crucially important for farm businesses in Suffolk and Essex. EU citizens play a key role in helping to grow our food, and they also fill many jobs within the wider food chain. This includes factories, food distribution, abattoirs and within the veterinary profession as well.

“Labour Force Survey estimates suggest 27,000 people from other EU member states worked in UK agriculture in 2016. A further 116,000 EU nationals worked in the UK’s food manufacturing sector. During peak seasons, the agriculture sector is further dependent on a large temporary workforce - thought to be around 75,000 strong - to supplement regular, permanent staff in harvesting crops. It is estimated that 98% of this number are recruited from other EU countries.

“These [figures] show evidence of an increasing shortage in the availability of seasonal labour, with predictions from labour providers that the issues and impacts of these shortages will be more pronounced this year, with the potential for supply chain disruption.

“We are calling on the Government to introduce a Seasonal Agricultural Workers Scheme, open to workers from outside the EU, as a matter of urgency, to give growers access to the employees they need to run their businesses.”

The Department for Work and Pensions said the figures should not be used to indicate immigration levels, as foreign nationals could have been in the country for some time before applying for an NI number.