What area of London has the telephone code 4479?

No, London has an area code of 020 for standard landline telephones.

However, +44 7xxx xxxxxx would be a United Kingdom mobile phone or personal number shown in international format. (07xxx xxxxxx domestically).

In the UK, mobile phones are not linked to geographic area codes - they are grouped together in the +44-7 (or '07' within UK) range regardless of location.