Britain should negotiate trade deals with individual US states as a backstop while Boris Johnson tries to seal a post-Brexit free trade agreement with America, a former trade secretary will say on Monday.

Liam Fox will point out that four US states - California, Texas, Florida and New York - would be members of the G20 if they were independent nations, and that many deals could be struck with states, rather than the US as a whole.

While tariffs on goods can only be negotiated by Washington, deals on services, which account for the majority of Britain’s transatlantic trade, can be sealed on a state level, unlocking billions of pounds of business for the UK economy.

Dr Fox will tell a conference in Geneva that free trade agreements are not “the only mechanism” to generate huge volumes of business between countries such as the UK and the US.

He will say that a comprehensive free trade agreement with the US will encounter “unavoidable difficulties” because “the US will, quite correctly, negotiate hard for its own interests” and “is likely to focus on better access for its agricultural products”.