<<With reduced separation on approach, it seems this needs to be sorted out...good question.>>
If tight spacing is employed it must be radar controlled. In such situations you fly the speeds given by the radar controller. If you are unable to accept them you must give warning in advance of final approach. I worked as a Heathrow Radar controller for 31 years and I could count on one hand the number of times a pilot told me he couldn't fly the speed I had given, usually due a weight problem.