Quotethe level of sterling depends on how well the Brits negotiate with Europe. If they get a deal like the outline of EU membership, sterling goes to 1.45 vs the dollar
If they don't , it goes between 1.20 and 1.30
the last time they negotiated trade seriously was 1973
I bet they drop Brexit
They will probably be happy with a lower exchange rate which can offset effect of any tariffs.
The only thing they probably really want to hold onto is passporting for financial services.