Many Japanese corporations have invested heavily in the UK, including global banking giant Nomura (NMR) and top automakers Toyota (TM), Nissan (NSANF) and Honda (HMC), CNN Money said in the report.
In a 15-page memo made public on Sunday during the G20 summit in China, Japan laid out its companies' demands for how the UK handles its "Brexit" from the EU.
Japanese firms saw the UK as "a gateway to Europe" when they invested there and now want reassurances that the country will seek to limit any "harmful effects" on their businesses, CNN Money reported citing the memo as saying.
Those with European headquarters in the UK may move those functions elsewhere in Europe "if EU laws cease to be applicable in Britain after its withdrawal," the memo warned.
Car makers, which often source auto parts from other parts of the EU for vehicles assembled in the UK, fear Brexit could add costs and delays to their European operations through customs duties at the border.
The extra charges and bureaucracy would have "a significant impact on their businesses", the memo noted.
