THERESA May will launch a major charm offensive in Japan today in a bid to begin the groundwork for a lucrative post-Brexit trade deal with the world’s third largest economy.

The Prime Minister will be accompanied by Liam Fox, the Trade Secretary, and a 15-strong group of business leaders from sectors, which already have a foothold in the country.

These include the Scotch Whisky Association, energy firm Amec Foster Wheeler, car manufacturer Aston Martin, and Barclays Capital Investment. Whisky exports are by far Scotland’s largest sale abroad, amounting to more than £4 billion last year. In 2015, exports to Japan, 14th in the export table, were worth around £80 million, an 18 per cent increase on the year before.

Mrs May’s spokeswoman explained: “Her main priorities for the visit include making progress on the shape of the post-Brexit trading relationship as well as exploring ways to boost the UK’s defence and security co-operation in the face of shared challenges.”

Underlying the importance of the three-day visit, Mrs May’s first as Prime Minister, are the nature of the organised events, which include: a defence briefing on Japan’s flagship aircraft carrier, Izumo, as well as attending a meeting of the National Security Council, a first for a European leader; a state banquet with Prime Minister Shinzo Abe and an audience in the Imperial City with Emperor Akihito.

No 10 pointed out that the PM would spend a considerable amount of “personal time” with Mr Abe, not only in bilateral talks but also at a traditional Japanese tea ceremony and joining him for a ride on the 180mph bullet train from Kyoto to Tokyo.

However, it has already been suggested that Mrs May could face disappointment in Japan as the country’s Government is concentrating on completing its trade deal with the EU, which it agreed in principle last month.

One Japanese Government insider admitted: “I don’t think there will be substantial progress. We haven’t finished [free trade] negotiations with the EU, just agreed at the political level, and many issues still remain.”

Elsewhere, Shinichi Iida, the minister for public diplomacy at the Japanese embassy, noted how Japanese businesses operating in the UK were "concerned" with the Brexit processes to come and said it was "no secret" the Government in Tokyo preferred a situation in which the UK would remain within the EU.

He noted: “Of course, we've been paying close attention to the Brexit negotiations and its relevant processes because there are 1,000 Japanese companies operating in the UK, which are creating 160,000 jobs; we have a big stake in it.”

Mr Lida added: "I'm sure Prime Minister May's visit and her assurance to be given to the Japanese businesses that the process will be transparent and the process and agreement will be of a phased approach…will be quite reassuring to the Japanese businesses and the Japanese Government as well."

But Sir Vince Cable, the Liberal Democrat leader, claimed Mrs May’s attempt to get an “EU-style” trade deal with Japan was absurd and that her visit to Japan had descended into farce before it had even begun.

He said the indication by Whitehall that ministers would seek a trade deal with Japan based on the existing EU-Japan deal was a “staggering statement,” which added a whole new level of absurdity to the UK’s negotiating strategy.

“It is now saying that the best trade deal we can possibly hope for with Japan post-Brexit is the trade deal we already have as a member of the EU,” declared Sir Vince.

"The likes of Liam Fox were promising a new dawn of improved trade deals but this clearly shows that even the Government now recognises that the best possible deal we can get with one of the world's largest economies is the deal negotiated by the EU,” he added.