London phone numbers are between eight and ten digits long. This includes a phone number of between six and seven digits, as well as an area code of between two and three digits, depending on where the caller is dialing from.
To call a number in London from outside the UK, begin by dialing 011 to open an international line. Dial 44, the country code for the UK. Next, dial the area code for London; this is 20 if calling from outside the UK, or 020 if calling from within the UK. Finally, dial the six or seven digit number of the desired party.