When did 01 telephone numbers start UK?

1959
The original UK '01' numbers were London numbers introduced in 1959. At this time, London was given 7-digit local numbers and the area code of 01. For example, London Transport had the number 01 222 1234. This system lasted for over 30 years.

1990
In May 1990, London was split into two area codes: 071 and 081, with the 01 code being withdrawn. Consequently, there were no numbers in the UK beginning 01 for the next five years.

1995
The national PhONEday renumbering saw all geographic area codes changed to start with '01'. Most areas just had a '1' inserted after the first '0', although some areas got completely new codes. For example, Swansea 0792 became 01792 while Bristol 0272 became 0117.

2000
The introduction of some new area codes, such as 024 for Coventry and 020 for London meant that geographical numbers could now start with either '02' or '01'. At this time, a more logical numbering pattern for the UK emerged:
01 and 02: geographical numbers
05: corporate business numbers
07: mobiles and personal numbering
08: freephone and special rate numbers
09: premium rate services