Sure, the Captain is ultimately responsible but at times ATC has to share part of that responsibility. When someone is being radar-vectored in IMC he can't be totally responsible 'cos he can't see what's happening outside.
On a number of occasions during my time at Heathrow I saw potentially dangerous situations saved by ATC: Several occasions when undercarriages were not lowered; once when an aircraft lined up with the adjacent main road in poor visibility.... again when an aircraft positioned itself visually to the wrong runway.... and if I had a pound for every aircraft approaching the old rwy 23 that started turning towards Notholt... These were no big deals. For one of the undercarriage affairs the controller got an air ticket from the airline, otherwise it was part of the job.
At the start of my career it was beaten into me (literally in those days) to a) check the runway visually before issuing a clearance, b) watch all take-offs until they were safely airborne and c) watch all landers throughout the flare and roll-out. I don't think it's written down anywhere in the UK, it's just the ATC version of "good airmanship", passed down from training officer to student, who later becomes a training officer, etc. I really feel for the controller in this incident but why I keep wondering why did he have to turn away and do admin at a critical time during such a quiet spell? It only takes a minute for a jet to line up and get airborne..