Japanese Prime Minister Shinzo Abe is likely to urge his British counterpart Theresa May to do everything she can to avoid a disorderly Brexit that some of Japan's leading companies have warned could be a disaster.
Japanese firms have invested more than 46 billion pounds ($A82 billion) in Britain, encouraged by successive British governments since Margaret Thatcher promising them a business-friendly base from which to trade across Europe.
The future of Brexit remains deeply uncertain - with options ranging from a disorderly exit from the EU to another membership referendum - because British lawmakers are expected on January 15 to vote down the deal May struck with the EU in November.
Abe had welcomed the deal and investors fear that if it is defeated then the world's fifth-largest economy would be plunged into a chaotic no-deal Brexit that would severely disrupt supply chains.
Abe and May will discuss the economic opportunities that exist for both nations as the UK leaves the European Union, Downing Street said ahead of the meeting.
"As the UK prepares to leave the EU, we raise our horizons towards the rest of the world. Our relationship with Japan is stronger than ever, and this visit will enhance co-operation in a wide range of areas."
For Abe, however, Britain's trading relationship with Europe after Brexit will be high on the agenda. He told reporters before his departure to Europe that he would convey Japan's position on Brexit to May.
When the two met at the G20 meeting in Buenos Aires in December, Abe asked for May's support to avoid a "no deal" and to ensure transparency, predictability and legal stability in the process.
Japanese carmakers Nissan, Toyota and Honda build roughly half of Britain's nearly 1.7 million cars and have warned about the loss of any free and unfettered trade with the European Union after Brexit.
The country's ambassador to Britain, Koji Tsuruoka, issued a blunt warning about Brexit in February when he said Japanese companies would have to leave Britain if trade barriers made them unprofitable.
"If there is no profitability of continuing operations in the UK - not Japanese only - then no private company can continue operations," he said.