Folks,
this proposal originally came from BA. Funnily enough, the points at which they proposed the 270 SLPs just happened to coincide with the EAT capture box for the TMA; in other words, BA (suits) were happy to fly balls-out to the capture box, then reduce speed to save a marginal amount of fuel (when compared to a transatlantic flight for instance), thereby guaranteeing their place in the queue. This matter was then raised at the OPA and the other airlines apparently agreed to it. The environment angle was introduced at a later stage, as initially the concern was the high cost of fuel.
As far as the speed restriction itself goes, it is NOT mandatory; ATCOs should only apply it in accordance with the current traffic situation. For example, if you have a bunch and are endeavouring to get them into a stream for the TC boys, then sod the 270kts - do what you have to do!
The first time i used the 270kts restriction, i had a BA pilot bitching at me about the reduction - not appreciated as i was very busy at the time. Said pilot was then advised (once the RT had quietened down a bit) about the origins of the restriction and sounded suitably embarrassed. Since then, i have refused to issue the instruction - if the airlines want this, why don't they instruct their pilots to do it and if it fits with my plans, great!!!
Quite frankly, whenever i can, i give 'when ready' clearances, thereby shifting the onus onto the flight deck to determine their optimum profile (i am not a pilot); unfortunately, sometimes i am unable to to do this and so have to use the ATC tools at my disposal to achieve a safe and orderly flow of traffic. It comes down to the fundamental question: efficiency vs capacity
With regard to the comment above about routeings, airspace changes/ old routes/new navigation: remember, it's not only Commercial Air Traffic that uses UK airspace - the military must also be given the space to do what they have to do, otherwise how can we as a country expect them to fight on our behalf? Also, any new airspace route changes are subject to the Airspace Change Process, which can be lengthy and costly, as well as being subject to public scrutiny - and let's face it, regardless of the environmental benefits a more direct route would realise, realistically, the general public only consider noise/visual pollution and have a 'Not In My Backyard' mentality.
Nuff said!