About USD and GBP
US Dollar (USD)
The US dollar is divided into 100 cents and is used in the United States and several other economies, and many tourist businesses elsewhere quote prices in dollars. When a card terminal in another country offers to charge you in dollars, that is usually a dynamic currency conversion with a poor rate; choose the local currency instead.
British Pound (GBP)
The pound sterling is divided into 100 pence and is used in the United Kingdom. Scottish and Northern Irish banks issue their own notes, which are valid but are sometimes refused in England, so spend them before you leave those regions. Contactless card payments are accepted almost everywhere, so you need little cash.
Exchanging USD for GBP
The rate above is the mid-market rate for USD to GBP. Banks, card networks and exchange desks usually apply a margin or a fee, so compare the amount you would actually receive. If a terminal offers to charge you in USD instead of GBP, decline: that conversion normally uses a worse rate.