Most stores and restaurants, theaters or travel agencies readily accept MasterCard, Visa and to some extent, American Express charge cards. The exchange rate at time of purchase will be used to calculate your charge in US dollars. Some independent Bureaux de Change will be open later hours, but often the rates will be higher. British currency is based on pounds and pence. There are 100 pence in a pound.
Coin come in various sizes.
If you decide to buy adapters in the US, check with either Radio Shack, Wal-Mart or any travel store. Consider using battery operated appliances whenever possible. The weather in England is normally warm and pleasant during July and August with some rain and cool nights. A sweater or wind-breaker will be comfortable on most evenings. You should be prepared for considerable rain and cool weather which may occur since the climate of England is a west-coast marine type similar to that of Washington and Oregon.