Once upon a time, London had a telephone code everyone knew and understood.
So much so that ITV's programme about events in the capital was called '01 for London'.
How things changed. The 01 code was replaced by two separate codes, 071 and 081, in 1990. These became 0171 and 0181 just five years later. The moves were intended to cope with the demand for new fax and phone numbers. Finally, London regained a single code in 2000: 020.
But it's the best kept secret in the capital. All but a few anoraks think London has two codes, 0207 and 0208. The confusion arose because the phone regulator added a 7 or an 8 to London phone numbers when it introduced 020. But most people think these numbers are part of the code, rather than part of the number. They're not. Does it matter? It does. If you're in central London and dial a number without the code, you'll get an unobtainable sound if you don't include the 7 in the number.
Last year the new regulator Ofcom claimed that the vast majority of London small businesses knew that the code was 020. It's hard to believe: a quick glance at shop front in one short street in Marylebone suggests that ignorance is the order of the day.