The independent research body's labour force survey estimated that around 761,000 (+96,000) non-UK nationals worked in those areas in 2016. The ONS said 508,000 (+69,000) of those employees come from the 27 other EU nations.
The British Retail Consortium, the trade association for UK retailers, has urged the government to avoid a clampdown,
"To meet consumer demand for home-grown food, retailers depend upon efficient domestic supply chains which have access to the right skills at the right time," a letter from the group and other organisations said in December.
"In order to meet this customer demand in the future, the UK's post-Brexit labour and immigration policy should be framed to enable domestic firms, including retailers themselves, to access the skills they need.
"We absolutely agree with the need to maintain a tariff-free trading relationship with the EU, which is necessary to retain access to EU and non-EU seasonal and permanent labour. Furthermore, not only would this help our exporters, but it will help retailers keep prices low for British consumers."
But Brexit pressure group Leave Means Leave has called for net migration, which was at 273,000 in the year to September 2016, to be slashed to 50,000 a year. Steven Woolfe MEP, the former Ukip migration spokesman, also backed a full five-year freeze on unskilled migration.
He argued that a post-Brexit visa should only be granted if the applicant has a job offer, is sponsored by a company and a minimum annual salary offer of £35,000; has passed a complete English language test; has a five-year private health insurance contract to prevent dependency on the NHS; and has a satisfactory level of savings.
"We need an immigration system that is fair, flexible and forward-thinking," Woolfe said. "It must be fair in its outlook, flexible in practice and forward thinking for our economy. Brexit is not about splendid isolation – it's about re-engaging with the world, without our wings clipped by the EU."
But such a policy would exclude tens of thousands of the non-UK nationals working in Britain's retail industry, which generates billions for the economy. An average annual salary for a retail worker in the UK in £27,520, according to jobs site Reed.co.uk. That pay bracket is £7,480 below Woolfe's threshold.
It is currently unclear what the UK's post-Brexit immigration system will look like since Theresa May has only recently started the two-year-long talks with Brussels. But the government has promised to reduced net migration to "tens of thousands", a pledge made in the Conservatives' 2015 general election manifesto.