tired,
Despite what Bright-Ling says there's nothing to stop Heathrow controllers saying, at an appropriate time, "when established on the localiser, descend on the ILS".
When landing on the 27's we can go from 4,000ft to 3,000ft at 13 miles out. If you're on a closing heading at that point and have only been told to establish on the loc, it can then be a good time to say "ABC123 descend to altitude 3,000ft, when established on the localiser descend on the ILS".
Nice and safe and works a treat. If we're concerned about any particular traffic under the approach, we always have the option of not saying it.
For your info the other descent restrictions on the 27's if you're not established on the loc are from 3,000ft to 2,5000ft at 11 miles out and from 2,500ft to 2,000ft at 9 miles out, all due to the volume of traffic (mainly heli's) below the approaches. We can't go lower than these profiles without having to make phone calls.
WF.