Big Ben not only tolls the hours, but it does so with a very distinctive noise. People all over the world recognise the sound before they hear the radio announcer say"This is London", or "This is the BBC World Service".
Probably because of London, which is also sited in the south east. The City of London is a very big city - employing many thousands of people. It makes sense, therefore, to live closer to London if you work there.