@ Flight Detent :
Or better yet, let's ask the other direction around:
If, by an ugly play of the devil, the ATCO working the runway would have a brain tumour moment and line up a plane in front of landing traffic just short of 3NM....
... what are the procedures in the UK to stop him from doing so?
(and while I trust 'oh that couldn't ever happen here', the point of the question is to hear why and how is that assured)
I am not and never worked in the UK, but until Brexit at least they worked the same as us , and then the answer to your question is simple , a controller is never alone , we follow ICAO 4 eyes porinciple , So incapacity of a controller,? the guy sitting next to him takes over. Plus in large Tower there is also normally a supervisor too.
One of the questions I asked ( not for here to answer ) is was the guy alone, and if yes ,was it officially planed by local management ( single Man ops due staff shortages ) or plain bad luck , e.g. toilet break, etc.. of the other.one.
I remenber Ueberlingen collsion in Zurich , the controler was also alone in his position ,and the Pilot of the DHL 757 was also alone in the cockpit when TCAS started.