I've been a controller for a few years (25 to be precise) although have never worked the LTMA.
My reading of Andrew's report is that controllers are being expected to sequence aircraft to the required minina (3nm/2.5nm/1000ft - take your pick). When I was taught how to keep blips apart it was beaten into us that these minima were precisely that, minima. There are lots of occasions where barely achieving that standard is about the only thing you should do. But, if the system relies upon a controller to constantly achieve the minima (ie no less and no more than) then it is inevitable that there will be losses of separation.
i heard an anecdotal story a few years back (don't know whether it was true of not) about a London controller (single runway south of HRW) who failed to validate in ADC because she only achieved a runway utilisation rate of 41 ac/hr as opposed to the 43 required. As I said, I don't know how true this was. However, the point is that the system required the controller to work, without and leeway, to two sets of criteria. On the one hand was the regulation, n the other hand was the commercial imperative. This is a similar scenario to airlines pushing crew scheduling to the absolute limit whilst staying within the law.
Somebody else has already said it. HRW has an outstanding reputation but one would think that 21st century technology could solve a lot of these issues.