London's
area codes have gone through
hell in the last ten years. We used to be 01. Then they needed more
numbers. So they split the city into inner 071 and outer 081. No, hang on, I can't even remember now. Didn't we have a stage where we were 0171 and 0181? Yes... no... who can tell... Yes, that was it, but I can no longer remember which was the earlier stage, 0171/0181 or 071/081, but one was needed as an intermediary to the other.
Anyway, nong43's point is that recently (a year or so ago) a wholly new area code was created, 020. At the same time all the seven-digit phone numbers in London were changed to eight digits, by the simple expedient of adding either 7 or 8 in front. This is part of the phone number, not the area code. You can't leave it out.
But, going by painted signs on shops and vans and sationery, approximately one half of Londoners believe it was another area code change, 020 becoming 0207, and if you're within the one zone the number is unchanged. Wrong.
A horrible cock-up all round.