Ex-President Obama’s chief trade negotiator Michael Froman. Reuters Former US President Barack Obama’s chief trade negotiator Michael Froman believes Britain won't seal a US trade deal anytime soon or even move talks to a "meaningful" stage until Brexit negotiations finish.

Froman said that while Prime Minister Theresa May has already started talking to the US about a bilateral deal ahead of Britain leaving the European Union, there are too many issues for the country to overcome before it can realistically expect a transatlantic deal to be signed.

Last month allies of US President Donald Trump told May that the two countries could "do a trade deal in a week," according to the Financial Times.

However, this is what Froman had to say to The Times in an interview (emphasis ours):

"That doesn’t mean that conversations can’t begin to happen — informal conversations about areas of sensitivity and priorities for the two economies. But there are some pretty fundamental issues that have to get resolved before that conversation can move to real negotiations.

"Even as the UK seeks to further trade with the US, it will want to maintain the deepest possible ties with the rest of the EU. Where there are differences between the European and the American approach to an issue, how the UK will square that circle — I think that is the biggest challenge. More than any one particular issue or sector.

"You need to know whether the UK is going to have sovereignty over its tariffs or whether products are going to be subject to the rules of a customs union. Is it [the UK] going to maintain all of the EU’s regulations going forward, such as quotas on audio-visual content? Is it going to have sovereignty over the digital economy regulations or is it going to defer to Brussels on that? Is it going to have sovereignty over sanitary and phytosanitary [plant disease control] standards, or other standards that can serve as technical barriers to trade?

"These regulatory and standards issues are a key part of our transatlantic economic relationship. Until those issues get sorted out, it’s very hard for the UK to commit to any agreement with the United States, or to really delve into any great detail about what a free trade agreement looks like."

Froman is the latest in a line of US, transatlantic, and EU trade experts to try and manage expectations of a UK and US transatlantic trade deal.

Last month Phil Levy, a former trade adviser to US President George W. Bush, told the Financial Times: "I think it is very unlikely that we see a deal soon. You have layers of complication with this."

Christophe Bondy from London law firm Volterra Fietta, who advised Canada in recent trade talks with the EU for its CETA deal, also told the FT that the US would need to know the full extent of what a Brexit deal will look like, before signing off on any deal, in order to "assess the full economic potential of a deal with Britain."

Canadian trade expert Jason Langrish, who helped "give birth" to the EU-Canada free trade deal, also said in January that "the next generation of bilateral agreements, of which CETA is the template, is complex.

"They reflect the realities of modern commerce and go beyond trade, touching upon behind-the-border issues such as standards, regulation, and opening government contracts to competitive bidding. This complexity means that the deals take years to negotiate and conclude. In our amped up media environment, there are special interests making noise at each step in the process, ensuring that trade and investment deals are a marathon, not a sprint."