The rate set by the Bank of England (www.practicallaw.com/A35892), and officially known as the Bank Rate, which determines how much other banks and building societies pay for loans they take out from the Bank of England.
The Monetary Policy Committee of the Bank of England meets monthly to decide at what rate the Bank Rate (or Bank of England base rate) should be set.
The term base rate is often used to refer to the base rate of individual financial institutions. If this is the case, reference will generally be to the base rate (from time to time) of a named institution. Typically this base rate will follow the Bank Rate, although there is no obligation to do so.