When did UK phone numbers get an '01' prefix rather than just '0'?

Question

So 0604 became 01604 etc?

Answer 1

In 1995, all UK geographical area codes were converted to begin with 01.  While most simply had the 1 inserted in their existing codes, a few were replaced with whole new codes.  These are the 011x codes.  As if the proliferation of non-existent 020x and 02xxx codes isn’t bad enough, there are even some people and businesses giving out numbers with ‘codes’ such as 01162, this is Leicester, for which the correct code is 0116.

Since 28 April 2001, almost all normal geographic numbers and most non-geographic numbers are 10 or 11 digits long.

The overall structure of the UK's National Numbering Plan is:

01 Geographic area codes.

02 Geographic area codes (introduced in 2000).

03 Nationwide non-geographic code, charged to caller at   geographic area code rates (introduced 2007).

04 Reserved.

05 Corporate numbering and VoIP services (note: some voip services use 08 or geographic numbers).

06 Reserved for possible use by Personal Numbering instead of 070 following consumer confusion with mobile phones.

07 Personal Numbering on 070, Pagers on 076, mobile phones on 075, 077, 078, and 079, WiFi numbers on 079112 and 079118.

08 Freephone (toll free) on 080, and Special Services (formerly local and national rate) on 084 and 087.

09 Premium Rate services.

Country Code: 44

International Call Prefix: 00

Answer 2

On "PhONEday", 16 April 1995, the digit "1" was inserted into all UK geographic area codes. Promotion of this day included special Easter Eggs. Under the new changes, for example, central London's 071 became 0171. This was with a view to reorganising the numbering plan, so that the first two digits would indicate the type of service called:

Answer 3

16 April 1995 - although some areas (such as Coventry) had their area code change shortly afterwards (in 2000) to 02