LONDON (Reuters) - U.S. Commerce Secretary Wilbur Ross said it was vital that a Brexit deal between Britain and the European Union would be in the commercial interests of the United States and London should not to give in to the EU’s “highly protectionist” trade stance.

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Ross was speaking at a British business conference on Monday which was dominated by the looming split between Britain and its EU neighbor, with firms stating their concerns about the impact on trade in goods and services. [L5N1NC1Q0]

British Prime Minister Theresa May’s government has placed great emphasis on the potential for a U.S. trade deal and bilateral deals with other non-EU countries, to allow it to flourish after leaving the bloc.

Ross said he hoped the United States could become Britain’s number one trading partner, citing already large trade flows between the two, but said U.S. interests must be taken into account when striking an exit deal with the EU.

“It is ... important that an eventual Brexit agreement takes into account our commercial interests, and does not hinder development of a closer post-Brexit U.S.-UK relationship by continuing divergent standards and regulations and other protectionist measures,” Ross said in a speech in London.

He criticized the EU’s external trade policy, including import tariffs higher than those in the United States and regulatory barriers, saying: “The EU talks free trade but actually is highly protectionist.”

But Ross was firm in response to a question about a trade dispute between Canadian planemaker Bombardier BBDb.TO and U.S. rival Boeing BA.N, which has prompted British political involvement by May to try to protect UK jobs.

The U.S. Department of Commerce last month imposed a 220-percent duty on Bombardier’s CSeries jets, whose wings are made at a plant in Belfast, following a complaint by Boeing which accuses Canada of unfairly subsidizing Bombardier.

“We understand the political sensitivity both here and in Canada, we understand about ... Northern Ireland - we get all that,” he said when asked about a preliminary ruling from the U.S. Department of Commerce.

“But the fundamentals remain: even our best friends really have to play by the rules.”