Boris Johnson is said to be planning a trade deal with President Donald Trump that would take effect immediately after the UK leaves the European Union on October 31.

Sources close to Johnson told The Times that Johnson, expected to become the next UK prime minister, planned to visit the US soon after assuming the role to strike a limited deal.

The UK's international trade secretary, however, says doing so would break the law.

The UK is prohibited from entering international trade negotiations while still an EU member.

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Boris Johnson's reported plans to reach a trade deal with President Donald Trump that would take effect as soon as Britain leaves the European Union are in "breach of European law," with a UK-US deal likely to take years to complete, the UK's international trade secretary has warned.

The Times reported on Monday that Johnson, the frontrunner to replace Theresa May as prime minister, planned to negotiate a deal with the US before the UK's October 31 scheduled exit date from the European Union.

"There is no question that the moment we leave on the 31st we should be in a position to get some kind of arrangement with the US," a source on Johnson's campaign told the paper.

But entering negotiations with a third country before Brexit would be in breach of the UK's treaty obligations as a member of the EU, International Trade Secretary Liam Fox said Monday.

"We can't negotiate anything with the US until after we have left the European Union," Fox told the BBC Radio 4 "Today" program on Monday.

"It would be in breach of European law for us to do that."

Read more: Insect-filled chocolates, rat-hair noodles, and maggoty orange juice: The reality of a Brexit trade deal with Trump

Read more: Trump says NHS must be 'on the table' in Brexit trade deal with UK



Sources close to Johnson suggested that the plan was to strike a "limited" deal with the US in just one area of goods.

But Fox, who campaigned for Brexit alongside Johnson, dismissed this, saying any deal would probably take years to pass through the US Congress.

"I've no idea what that would be," Fox told the BBC of a so-called limited deal.

"That will take time, and you have got the added complication, just remember, we are now getting very close to the American preelection year where it is quite hard to get things through Congress, so even if you negotiate them quickly, you wouldn't be able to ratify them."

Last month Fox also dismissed Johnson's claim that the UK could use an international trading rule called "GATT 24" to keep trading with the EU on zero tariffs in the event of a no-deal Brexit.

"It is important that public debate on this topic is conducted on the basis of fact rather than supposition," he said.

Johnson has previously sought to downplay fears about a US trade deal weakening UK food and agricultural standards.

Under US food standards, products can contain certain amounts of foreign bodies, including maggots, insect fragments, and mold.

For example, US producers are allowed to include up to 30 insect fragments in a 100-gram jar of peanut butter, as well as 11 rodent hairs in a 25-gram container of paprika or 3 milligrams of mammalian excreta (typically rat or mouse excrement) per each pound of ginger.

Johnson has recently sought to downplay such fears by insisting that he would demand the US meet UK standards instead as part of any deal.

But Fox dismissed this, telling the BBC: "If you go to the US and say we are going to take any discussions on agricultural access off the table, they will close down pretty quickly."

Fears about the National Health Service also being included within a trade deal were heightened recently when Trump told reporters during his recent state visit to the UK that it would be "on the table" in trade talks.

Trump later withdrew the comment.