There seems to be a problem at the moment with signallers giving priority to the "wrong" trains, ie. putting a "stopper" in front of a "fast", especially on the northbound approach to Blackfriars. It isn't much of a problem through the Core, but north of StP, unless the "fast" can get onto the down fast line, it can be baulked all the way up to St Albans and beyond, thus getting progressively more delayed through the journey.
Are these signalling decisions taken by the human or by some clever computer algorithm? I ask because the decison should take into account whether delaying a stopper by 2 mins to allow an already delayed fast through could result in the fast making up time whilst the stopper must have additional slack in its timings that could easily recover a couple of lost minutes.
By the way, in response to the comment about putting a 442 on the London Bridge service, I'd be happy to ride a 442 on a fast BedPan service (subject to the necessary AC mods) in place of the "Spartan-Spec" 387 or "Dustbin-Spec" 319.