Dan please do not comment emotively on subjects you are not directly involved in! Are you a Heathrow Tower Controller? Thought not! Vortex separation is a safety matter and is not taken lightly. 120 seconds vortex separation is applied - it is perfectly legitimate to take into account the take off roll which takes 40 - 50 seconds, as vortex is not produced until the nosewheel lifts off the ground. The two mile rule is, as has been stated a DEPARTURE separation - not a vortex separation and can only be applied between aircraft on diverging routes. In the USA they can apply five miles vortex separation on departure for vortex but not in the UK. Any departure separation based on time is only designed to achieve one aim - five miles separation on radar on the same route.
"Up to the pilot to decide whether he values his life sufficient to delay departure or not (I don't know if anybody would admit this though)" - just what are you implying here? An emotivre and unhelpful statement.
Vortex spacings are minima - if a pilot wishes to delay departure because he feels that the vortex separation being applied is insufficient, he is within his rights to do so! (We prefer to be told if more than the UK standard of 1 minute for a Lower Medium behind a B757 is required so we can adjust the departure order if necessary).
Separations not based on vortex wake are NOT being reduced!!! The 2.5 nm spacing procedure is perfectly safe in the appropriate weather conditions, and merely caters for the situation we had in the past when aircraft initially 3nm apart reduced to 2.5 nm apart within 4 nm from touchdown, due to differing final approach speeds or different rates of speed reduction. All the Heathrow procedures are closely monitored by the Safety Regulation Group of the CAA. Are you suggesting that the CAA are approving unsafe practises? "Wheels up" take off clearances are perfectly safe - I have been using them for 25 years without a glitch. When both aircraft are the same weight category and their tracks diverge by 45 degrees or more there is absolutely no problem! If we waited for the full one or two minutes between departures the airport would grind to a halt and operations would be no safer than they are now. As Stansted develops and has freeflow departures, as will happen, I am sure that they will adopt similar procedures.