In other cases I would consider the term 'downtown' to be the oldest portion of the city. For example in Philadelphia. This would be much harder to pick out in a city like London that's much older.
I live in Washington DC. Here, the term is only used when you are outside of DC and it is used loosely to describe any location inside of DC. If you were in Virginia or Maryland and said you were going 'downtown' that would mean only that you were going to any location inside Washington DC.
I'm a strange city I would assume the term downtown referred to the less kept more rustic area that looks kind of ghetto but is a little more artsy/trendy than the rest of the city.
You're suggesting that downtown is Oxford & Regent Streets, i.e. essentially high-street fashion shopping. Thing is, almost every shop on those streets is also in both Westfield malls on either side of the city, and many of the bigger brands are also on dozens of high streets across the city. There's seldom much call for most Londoners to actually go to those streets (IMO).
In a business context, downtown in London is the City, but the tallest buildings aren't in the City, they're in Canary Wharf, a privately owned near-island with 24-hour guards at all entry points, and barriers that go up on the roads at night.
Not to nitpick but this isn't strictly true. The tallest building is in neither but very close to the City, then the 2nd tallest is in Canary Wharf but the third and fourth are definitely in the City again. You have some in the Wharf and some in the City after that but I am not sure if the difference regarding skyscrapers in the 2 parts is very relevant or explicit anymore.
Well, part of it is, but West End office rents are a lot higher than City rents.
Other than that, I totally agree: London doesn't really have a centre
Which part would that be?
I don't mean to snark, that's not a meaningful phrase to this englishman with 10 years London living under his belt. I actually struggle with definitions of downtown or uptown, it's not something we would say. How do they apply to (for instance) NYC which I'm a little familiar with?
--edit-- yes I am drunk and this is a stupid question :)