It will cost you a minimum of 10c from a pay phone but much more from a hotel room. Unlike the US you pay per minute for every call no matter where you are calling. There are three different calling zones in the United Kingdom, Local, Regional and National. There are also two different time rates 8am to 6pm being the more expensive and 6pm till 8am being the less expensive.
0800 calls are toll free and 01 numbers are regional or national calls, all others are charged at various rates and can be expensive. Examples include 0890 numbers, which currently cost 49c per minute.
It is recommended that you check with your hotel to see how much your calls are going to cost you before you dial.
International directory enquiries: 153.
UK (except London) directory enquiries: 192
London directory enquiries: 142