Interesting to see where this leads.
By "no third runway" does Vince mean "for the term of this (coalition) government."
The answer to SE capacity surely changes dependent upon the timescale you set.
If you require expansion and the criteria is 3-5 years; then mixed-mode or third runway is the simplest answer. *Discounting Stanstead and Luton at this point.
The problem with Heathrow is not the location of the Airport; what the objection boils down to is the West London flight path.
Personally, I believe a third runway, steeper approaches, RNAV/MLS coordination and partly inset thresholds would be win-win for proponents and opposers.
Others have mentioned the irony of the stance of Goldsmith and his ilk arguing to reduce noise and achieving wantonly wasteful holding times and the necessity for mixed mode to be considered! ...Bonkers.
If the Government choose to write-off Heathrow development indefinitely, then the timescale required to allow for new airport planning, protests inquiries and development would undoubtedly be to the detriment of UK plc.
The Thames Airport is the wrong side of London as long as London stays in the bottom right hand corner of the UK map. It's not inconceivable that this proposal could work as a hub: building the runways, parking the aeroplanes and routing flights is workable. But! ...the infrastructure required to move a significant number of passengers around the capital is the trick.
What cost (time and financial) of the high speed rail network linking the UK south to the terminals in the estuary??? Can we even afford this right now. Without being flippant, people do like to drive to airports with luggage rather than get a bus to the train station to get a train and change trains and arrive at the terminal - you get what I mean I'm sure.
A new airport to the West would be a sensible long term plan, after the third runway has solved our immediate crisis. The economics should really shine through and common sense should prevail...(?)
How about 2 parallel perpendicular(ish) runways over the reservoirs on the far side of the M25?
As long as crosswinds permit you'd lose the approach noise problem. Not sure how you'd coordinate take-offs on the westerlies with go-around traffic - but I'm not an airport designer....