Boris Johnson must use talks with President Donald Trump this week to protect British farmers and consumers in any post-Brexit trade deal with the US, the Liberal Democrats have said.

Party leader Jo Swinson is calling on the Prime Minister to make sure discussions on the sidelines of a Nato summit in London make clear the UK will maintain its food standards.

Ms Swinson claims that leaked documents from UK-US trade talks show American officials are pushing for Britain to allow greater use of chemicals in food production.

This would include chlorine-washing chicken and growth hormones in beef cattle, according to the Lib Dems.