New telephone users in London are to be given an 020 3 prefix to meet the increasing demand for new lines.
The new 020 3 prefix will be issued next year
Communications watchdog, Ofcom, said there would be no change to existing numbers starting with 020 7 and 020 8 which would continue to be issued.
The watchdog said multiple occupancy flats and new businesses have driven up demand and the new prefix is due to come into use next summer.
About 400,000 new numbers are allocated each year in the capital.
The 020 7 and 020 8 codes for Greater London were introduced during the Big Number change of 2000.
Ofcom's Matt Peacock said the stash of 020 7 numbers are expected to start running low by next autumn.