Hi
F4mandolin - to move large amounts of funds over, you'll need to look at currency exchange specialists like HiFx and Moneycorp. These specialists have better exchange rates than you'll find anywhere else along with other useful aspects etc.
Et al, whichever way the referendum goes, there's going to be economic uncertainty as various aspects get discussed. For individuals looking to exchange currencies between the US and UK, using a currency specialist will at least get the best available rates at the time of requirement (ideally, anyone needing foreign currency should do so asap!) . If aspects are resolved relatively quickly in the political world, then the world's markets will respond perhaps more favourably. If various aspects in the political world get convoluted and messy, then everyone should expect more financial issues in everyday life.
Cheers, DtM! West London & Slough UK!