I would say that the low transition altitude and level in the UK contributes to some altitude busts since you reset QNH or QNE in the terminal area at times of high workload and traffic. Also, clearances to levels and altitudes near the transition layer are common, some companies reset the altimeter when a clearance across the layer is received, others wait until crossing the layer lest the controller ask for "passing altitude". Just when you reach for that altimeter knob, you inevitably get a vector or another altitude constraint, it's the nature of the game in busy airspace down low.
I was always taught, that when cleared from an alt to an FL, or vice versa that you reset the altimeter BEFORE starting to climb / descend, to avoid just this sort of problem.
Obviously if the initial departure clearance is to an FL then one needs to remember to set QNE, but I can't see why one would have to wait till actually passing the transition level? in any case you have the standby which will probably be on QNH anyway, in order to read back a passing level if required.
Anyhoo - re the increase in level busts - is this due to LATCC changing their reporting criteria last year? or maybe trying to squeeze a quart into a pint pot is finally causing the system to creak at the seams?