President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Tuesday promised the United Kingdom a “very, very substantial trade deal.”

“We're going to be working on that today and even a little bit tomorrow and probably into the next couple of weeks,” Trump said in remarks before a business roundtable at St. James's Palace in London. “But I think we'll have a very, very substantial trade deal.”

Trump also seemed to suggest that the U.K.'s plan to leave the European Union presented an opportunity for closer trade ties with the U.S.

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“And there's an opportunity — I think a great opportunity — to greatly enlarge that, especially now, in light of what's happening, to tremendously enlarge it and make it a much bigger trading relationship,” he said.

Outgoing U.K. Prime Minister Theresa May Theresa Mary MayAre US-Japan relations on the rocks? Trump insulted UK's May, called Germany's Merkel 'stupid' in calls: report Bolton says Boris Johnson is 'playing Trump like a fiddle' MORE also made clear she was interested in pushing toward a deeper economic relationship with the U.S.

“It's a great partnership, but I think it's a partnership that we can take even further,” she said, speaking before Trump at the roundtable.

“Of course, that's with a good bilateral trade agreement but also, I think, building a wider economic partnership for the future as well, and working together and continuing to work together in underpinning, shaping, and influencing the global economy, the rules on which that's based, and its institution because we believe in keeping markets free, fair, and open, and keeping our industries and our businesses competitive.”

May is set to step down as prime minister on June 7 after failing to secure a Brexit deal.

That complicates any potential trade negotiations, as the deadline for Brexit has been pushed back until October.

Many of Britain’s trade policies going forward will be dependent on the conditions of its departure from the European Union, making ironing out a trade deal before then difficult.

In 2018, the Trump administration placed 25 percent tax on steel imports and 10 percent tax on aluminum imports from several nations, including the U.K.

May called the tariffs “unjustified” at the time.

A number of U.K. companies were among hundreds that received waivers from the administration on the steel and aluminum tariffs.