If disturbing Her Majesty was the only major issue, why not land on 09R and take off from 27R? I am not an airline pilot so I don't know if that would be against the rules due to planes taking off in the same direction as approach. But, if I was in control, I'd just have all flights from 27R immediately change course to 000 after gear up.
EDIT: NOT A RIP ON LONDON... but why did they opt for building so many airports with just a couple of runways??? Atlanta and JFK both have 4. Heck even Cleveland (KCLE) has 4.
answer 1: the reason why they don't land/take off on the runways you said, is simple: noise. If you TO from 27R, your jetblast and all that noise would go directly to Her Majesty, and the reverser noise on landing would do the same. the reason why they don't change heading right away is because they can't turn that fast and the way you described. If you did that they would fly right over the terminal, and possibly over other noise-restricted areas.
answer 2: the reason why is exactly what NorgeFly said: environmentalists. (i love how we have "mental" in there.....makes them sound stupid
) people are too close to LHR, LGW, STN, LTN and LCY to fit a third runway in there......and also people don't want to move from their "ideal" location right beside the busiest airport in the UK.......especially right beside one of only 2 runways.....
stupid people. if they complain about delays, cancellations and whatnot but "don't want to move out of the way for a third runway" because they want to stay there instead of go through the trouble of moving, is beyond me. It's kind of stupid of them really; you don't want to move away from your small house adjacent to the busiest airport in the UK and right beside one of only TWO runways servicing it, and you complain about the noise too because there is "too much traffic in the air", yet you complain to the government about the fact that the delays at THE BUSIEST AIRPORT IN THE UK are too excessive because the TWO RUNWAYS are getting far too clogged and noise-restricted, and yet when you want to go somewhere, your flight is delayed and you get extremely mad. All of that, because you don't want to move away from the busiest airport in the UK so that your frustration towards delays and cancellations can be eased. Seriously, JUST BLOODY MOVE AND STOP WHINING!!!!!!!!
huh....that was long and confusing
(btw, no offense is meant towards the UK, LHR (and LGW), Her Majesty's Government or any residents of the UK in the general London area