World leaders have taken the opportunity of the G20 summit to tell Britain's new prime minister their thoughts on Brexit, ten weeks after the U.K. voted to leave the European Union.

President Barack Obama during the G20 summit in Hangzhou, China reiterated the stance that the U.K. will be at the back of the line for new trade deals after the Brexit vote. He said the U.S.'s first priority would be to finalize the Trans-Pacific Partnership and to progress on a deal with Europe.

Obama added that there was no point in trying to ink a deal with Britain, until a proper deal between the U.K. and Europe had been arranged.

But he said there does not want there to be any adverse effects on trade between the U.K. and the U.S. arising from the Brexit vote.

"We are going to do everything we can to make sure the consequences of this decision [Brexit] don't unravel what is already a very strong and robust international relationship," he said.

Separately, the government of Japan has warned that Japanese companies would leave the U.K. if negotiations with the EU don't go as planned.

A memo to the U.K. posted on Japan's foreign ministry website over the weekend stated that Japanese companies invested in Britain because the country is seen as a gateway to Europe.

"We strongly request that the UK will consider this fact seriously and respond in a responsible manner to minimise any harmful effects on these businesses," the memo said. "Japanese businesses with their European headquarters in the UK may decide to transfer their head-office function to continental Europe if EU laws cease to be applicable in the UK after its withdrawal."

The memo called for transparency in the U.K.-EU negotiation process, asking for clarity on the "whole picture of the Brexit process as early as possible."

Japan expressed significant concern over financial institutions that may lose their passporting rights, which allow companies to be headquartered in the U.K. but to sell their services across the European Economic Area.

Even though dire warnings continue about Brexit, economic indicators have suggested the U.K. economy has withstood the shock. 

Data out from Markit/CIPS  show that the service sector rebounded in August. The business activity index was at 52.9 in August up from 47.4 in July.

The pound was recently up 0.3% on the dollar at $1.3334.

The FTSE 100 was recently down 0.21% at 6,880.09.