[rswail]

Except that the UK is a small island off the side of the third largest trading bloc in the world. Why would anyone want to negotiate only with the UK?

Why would Japanese companies want to continue to manufacture vehicles in the UK when it will only support its local market?

The UK is a relatively small market, its only advantages were stability (now lost), having the City (a tax haven, with branches in British off-shore locations), and access to the EU.

You've still got the City, but EU finance will move to other capitals.