European agriculture commissioner Phil Hogan has warned London that EU subsidies will end in 2020 because of Brexit and it will then be up to the British government to support its farmers.

Hogan, who is Ireland's commissioner, told AFP in an interview on Wednesday that there would be no extension to the farm payments that have been agreed under the EU's Common Agricultural Policy.

"I have been assuring farmers in the UK that our payments will continue as they are now until 2020," Hogan said in Brussels.

"Then it's a matter for the British government, on the assumption that the negotiations are concluded, that they will be able to fund all the various farming measures that they wish... from their own resources."

The EU subsidies are legally bound to continue until 2020 despite the fact that British Prime Minister Theresa May's timetable sees the country leaving the EU in early 2019.

Officials from British farming and food industry groups met with British government ministers this week amid fears about how their heavily subsidised sector will cope after Brexit.

Hogan added: "Of course farmers are worried about this but it's a matter for their own government... I have given them the assurance until 2020 and it's up to the UK government to give them the assurances beyond that."

British finance minister Philip Hammond pledged in August to match EU funding for farmers, universities and infrastructure projects after Brexit to 2020 but has given no details of what happens afterwards.

- Seasonal workers -

Hogan meanwhile urged Britain to be "mindful" of the issue of seasonal agricultural workers, following a sharp fall in the number coming to Britain.

"The PM (May) has made it perfectly clear that she wants to have a strong political position on the immigration issues," he said.

"But of course (we) expect that she will be mindful as well of the requirement of many farmers and agribusinesses for seasonal workers which are essential for the viability of their businesses."

But the commissioner added that it was up to Britain to find the solution.

"It's not the responsibility anymore of the EU because we didn't cause this particular issue to be a major issue, and neither are we involved in the solution to this problem which has been created by the British government," he said.

Hogan meanwhile said he was "working with the Irish authorities" to minimise the impact of Brexit, as Irish farming is highly dependent on British exports with 41 percent of all the country's farming exports going to Britain.