The use of incorrectly printed dialling codes drives me insane! 

Classic example as you have shown is London - 020. 

London has never had an 020X code.  0203/0207/0208 are not dialling codes, yet business' across London and further afield continue to use that format! 

I recently found a "budget" Supermarket who have started a new format of Warehouse style outlets, who have listed their Old Kent Road (London) venue as 02036 xxxxxx (instead of 020 36xx xxxx).  Equally they have put Leicester (0116) as 01162 xxxxxx.

The mind boggles! 

Ian01 I wish this forum possessed a "Like" or Thumbs Up button 

The US phone system gives just under nine million numbers per area code, meaning that the physical area of some area codes is very small. Others cover a vast area but still with hardly any numbers in use. The worst problem is that some areas have multiple area codes.

The original system allowed for less than 200 area codes as area codes had to take the form x0x or x1x. This has subsequently been expanded to allow other formats. Another issue is that several dozen area codes are charged at international rates as they are for nations in the Caribbean.

The UK phone system sees each area code cover roughly the same size physical area, but with a different length of local number to cope with the different population densities. Areas generally each have either a eight-hundred thousand or eight million numbers. The 02 area codes each have room for eighty million numbers, and it was a mistake to issue those in places other than London and NI. There's a small number of areas with eighty-thousand local numbers. The general formatting rules aren't particularly difficult to remember and some mobile phones auto-format the number for display as it is dialled.

The UK has room for around eight hundred geographic areas codes with vast amounts of additional space for mobile numbers, non-geographic numbers, and space for further expansion.