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MEXICO CITY (Reuters) - If the United Kingdom leaves the European Union without a deal it could have “very significant” costs for some parts of the British economy, Roberto Azevedo, Director-General of the World Trade Organisation (WTO), said on Thursday.

The British government is scrambling to find parliamentary consensus over the terms of its departure from the European Union ahead of an April 12 deadline, prompting warnings from some officials that the risk of a no-deal exit is increasing.

Azevedo said in Mexico City that economists were best placed to estimate the potential impact of a no-deal Brexit, which would leave the British economy trading on WTO rules.

“But I would say there will be costs, and the costs may be very significant in some sectors, and maybe less significant in other sectors. But overall, there will be an impact, we all know that,” he told Reuters in an interview.

Separately, Azevedo sounded a note of caution on ongoing efforts to resolve a dispute over the future of the WTO’s Appellate Body, the top court of global trade.

Washington has long argued that WTO judges have routinely broken with procedures and exceeded their mandates, and in a bid to force reforms, the U.S. government has blocked the appointment of judges to the Appellate Body.

If continued, the tactic could render the body inoperable by December, when terms end for two of the remaining three judges. Under WTO rules, three judges are required to hear appeals.

Azevedo said WTO member states were seeking to find a way around the impasse, noting that it was chiefly a U.S. concern.

“The truth is that it’s difficult to know if we’re advancing or not,” he said, “because the Americans haven’t been contributing in a very active way to these discussions.”