Whilst it’s difficult to assume anything, overseas travellers might consider taking $US on their holidays to exchange rather than the £UK. When Brexit was announced around two years ago, in Asian countries it was difficult to exchange the British pound, as each day the currency was losing value.
An exchange office for example, might lose money by giving you an exchange rate one day, that drops significantly the next. Many bureaus would not take pounds. Whilst it’s impossible to know what will happen to exchange rates or the stability of the Pound around Brexit, those travellers wishing to minimise their risk might consider the dollar.