Reading this, I've had a thought.
IF we assume that the exchange rates were to stay the same for a while, (and I doubt that), then what we export to Europe will be cheaper, (for them), so we should be able to export more.
What they sell to us will be correspondingly more expensive, so we are likely to import less.
So our balance of payments improves.
And, as long as the exchange rate stays the same, this situation would continue till such time as we officially left.
ALTOGATHER NOW---
Lets look for the Silver ling.