Re: Wrong dialling code
The BT phone book here tells you what the STD code for London is:
The answer is '020'
There is no 'inner' and 'outer' any more. The number that corresponds with what used to be the local exchange is now defined as having four digits, and can start with a 7, or an 8, or indeed a 3 since 2005. So London numbers can be
020 3xxx yyyy
020 7xxx yyyy
020 8xxx yyyy
...and indeed it is expected that all the other digits can be used in that leading position.
Full details of the UK telephone numbering plan are published by Ofcom here:
which can be found on this page:
There is a Wikipedia page dedicated to misconceptions about the numbering plan: