More than 100 farming and food industry bodies have united to make a series of policy demands to the prime minister – including to ensure they can continue to hire vital overseas workers after Brexit.

The 'food supply chain manifesto' has been agreed by key industry players including the leaders of the National Farmers' Union (NFU), the British Retail Consortium, and the Food and Drink Federation, as well as various farming sector bodies, seed companies, agronomy firms, grain traders and agrochemical suppliers.

With many food and farming businesses relying heavily on EU workers, the document urges the government to publish an immigration white paper setting out its post-Brexit plans as soon as possible.

Other issues raised include:

• Maintaining 'frictionless' trade with the EU and preserving the existing trade deals struck by Brussels with countries around the world – at least until the UK can secure acceptable alternatives.

• Developing an agriculture policy which promotes food production while maintaining existing high environmental, health and animal welfare standards.

• Ensuring an 'efficient and proportionate' regulatory system.

The manifesto has been sent to Theresa May by NFU president Minette Batters, who said the food and farming sector was worth at least £112bn to the UK economy and employs around four million people.

'In the manifesto we warn, as a collective, that a Brexit that fails to champion UK food producers, and the businesses that rely on them, will be bad for the country's landscape, the economy and, critically, our society.

'Conversely, if we get this right, we can all contribute to making Brexit a success for producers, food businesses and the British public, improving productivity, creating jobs and establishing a more sustainable food supply system.'

The manifesto says 'with a significant proportion of EU nationals working in the UK agri-food sector, it is vital that the government ensures a continuing, adequate supply of permanent and seasonal labour for the industry before and after the UK leaves the EU'.

It adds that 'many of our businesses are experiencing difficulties in recruiting staff from within the UK' and consequently the government must ensure that 'in the short- to medium-term the industry has access to the overseas labour market to help meet its recruitment needs'.

A government spokesman said: 'We have been clear that up until December 2020, employers in the agricultural and food processing sectors will be free to recruit EU citizens to fill vacancies and those arriving to work will be able to stay in the UK afterwards.

'We are determined to get the best deal for the UK in our EU negotiations, not least for our world-leading food and farming industry which is a key part of our economic success.'