Quite agree that this is an accident (or a very near miss) waiting to happen. It's not a UK thing, it's come from ICAO and they need to re-think this and change it. The only way it will work is for new levels never to issued until the aircraft is past the restriction point or for the SID restriction to be cancelled every time when issuing the level.
In the same way as the phrase "take-off" is never used by aircraft or ATC except to actually issue the take-off clearance the same should apply to "climb" or "descend". The phrase should never be used except when it is safe for the aircraft to follow the clearance. Another piece of madness dreamt up in an ivory tower by people who have probably never been near an ATC radar unit or an aircraft.
It's basically a conditional clearance and I thought that was something ICAO where trying to get away from, very strange.