I have had the pleasure of changing terminals at London Heathrow and think of it not as one airport, but as three: One is formed by T1, T2 & T3; there is a second at T4; and now a third at T5. All three airports are served by two runways quite near each other. Building a third runway north of the M4 motorway will not change that.
Why do I think it's three separate airports? The published minimum connecting times (MCTs) would seem to confirm it:
- LHR T1 to T4 = 1h 30m
- LHR T1 to T5 = 2h
- LHR T4 to T5 = 2h
- LHR to LGW = 2h 30m
- GLA to PIK = 2h
- FCO to CIA = 1h 30m
- OTP to BBU = 1h 40m
- ARN to BMA = 2h
CDG and MAD also suffer from some long inter-terminal changes. But MCTs at AMS are 50m and at FRA 45m. LHR seems to have lost out, probably a victim of its original design. Time to make a fresh start at STN, I think, as other posters have suggested. Keep LHR as a regional airport for West London and Berkshire.