Ten bucks says that the balance of trade between Japan and Britain is strongly in Japan’s favor as it is.And yet they want more.
you are correct — from 2019 numbers,
Imports to UK 14,163
Exports from UK 13,531
Total trade 27,694
Trade balance -632
The thing is - they can see that the UK is weak and getting weaker. Plus, with the UK leaving the EU, Japanese companies will move operations from the UK (which was their base into the EU market), so Japan wants to get other items to compensate