Broadly speaking Heathrow is London’s hub airport, Gatwick is its primary leisure airport (scheduled and charter), while Stansted and Luton major on the low-costs. London City has its own unique attractions and limitations, and Southend is just chasing what’s left.
Broadly speaking yes. But also:
Gatwick is the regional airport for most of Sussex, Kent, Surrey, Hampshire and a good chunk of South London.
Stansted is the regional airport for most of East Anglia, Essex, and NE London.
Luton is the regional airport for the three counties (Beds, Bucks, Herts), Northants, and NW London.
Each of these areas has a population bigger than of Scotland. My point is that even if central London didn’t exist, these airports would still be doing a decent trade with traffic from their hinterland.
Southend is of course the regional airport for, err, Southend, Billericay and Brentwood. Which is why flights from there are almost exclusively to the Med to top up that tan
You are complaining about "ripping up Middlesex" but your HSM25 High Speed Heathrow to Gatwick Railway would probably end up requiring more demolition
Quite. I think in terms of localised environmental impact, a High Speed line through the North Downs and some rather lovely (and well heeled) parts of Surrey is at least two orders of magnitude more damaging - and difficult to get consent for - than a third runway through Harmondsworth.
I write as someone who caryoned an imaginary Manchester - Birmingham - London High Speed line with a branch from near Chalfont to Heathrow and Gatwick back in 1988. I still have the map.