Rams
aspiring to be like Ryan Giggs
The EU is not going to cease trading with the UK if the UK introduces visa requirements, in the same way that the rest of the world trades with the UK despite having visa requirements when their national come to the UK and vice versa. It doesn't stop EU nationals from living and working in the UK, only gives the UK some degree of control of who comes to the UK.
It won't cease trading with the UK, but the UK will only be able to trade on terms far more unfavorable than countries or regions that have made concessions in terms of immigration or visa entry. Besides, without such concessions the London financial market will be in a right state.