But there are other interesting things: UK citizens may face higher transaction cost to/from Europe, and especially small consumers will get more trouble with import taxes, i.e: a maximum amount they can spend tax-free each year.
(European consumers can now spend a relatively small amount in the US. Pass that limit, and substantial taxes (~20%) are added.)
UK citizens may also spend more in other countries in the world, now they are similarly priced to products for Europe (especially from China)
More worldwide payments that need to be cheap and fast for small payments, is good for bitcoin.
I think these 3 have more effect on BTC than the rate of the pound.