The forecasts are based on the 15-year impact of staying in the single market, doing a trade deal with the EU, or exiting the union with no deal.
But speaking to Sky News after the meeting, Japan's ambassador to London Koji Tsuruoka warned of the "high stakes" of Brexit.
While companies are eager for extra detail on what kind of Brexit the Conservatives want, Japanese banks have started to adjust their operations in preparation for the loss of financial passporting rights following the divorce.
"So, it's as simple as that".
Nissan, Toyota and other Japanese companies will be discussing their investments in Britain during a meeting with Prime Minister Theresa May and Treasury chief Philip Hammond.
Quizzed on the Government's own Brexit impact assessment leaked to Sky News that showed regions in the United Kingdom could suffer a hit to GDP of up to 16% over 15 years, the Brexit Secretary played down the report. A Downing Street spokesman did not offer an immediate comment.
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The injured have been transported to local hospitals, and officials confirm everyone has been removed from the trains. The President tweeted: "My thoughts and prayers are with all the victims of this morning's train collision in SC ".
Nissan sought assurances over post-Brexit arrangements ahead of future investment in the Sunderland plant, Britain's biggest auto factory.
But analysts said there will not likely be much progress until Japan and the European Union wrap up a nearly-finalised trade deal, and details of Brexit are worked out.
"Japanese businesses with their European headquarters in the United Kingdom may decide to transfer their head-office function to continental Europe if EU laws cease to be applicable in the United Kingdom after its withdrawal", said the 15-page document.
With over 1,000 Japanese businesses in the United Kingdom, the country is the UK's 11th largest trading partner, with investment into Britain reaching £46.5 billion in 2016.
"Uncertainty is a major concern for an economy", it said.