It all depends what you mean by 'steep' though, doesn't it?
Quite so. We're talking here about the Policy Exchange proposal, which specifically refers to 5.5° approaches for all narrow-bodies using LHR.
"We anticipate that by the time the new Heathrow airport opens it would be possible to have a standard descent approach for narrow bodied planes of 5.5 degrees."
Bigger and Quieter: The right answer for aviation