In the UK, unless you use the words PAN PAN PAN or MAYDAY, you will not be afforded any priority if you have an emergency of any type and that includes fuel.
It was bought in many years ago after a series of incidents where pilots would say or intimate they were short of fuel, just to get in ahead of anyone else.
I am not suggesting that this was the case here, far from it, had I been on duty I would have afforded the aircraft the utmost priority and then, after the event was done and dusted, gone out of my way to ensure that every angle of their performance was examined in the minutist detail.
Their failure to declare an emergency goes against the most basic of ICAO procedures and is probably a reflection of their airlines operating procedures.
As for demoting the ATC staff with the benefit of hindsight, I come back to my original point, the crew didn't act in accordance with International (ICAO) procedures, so it's the crew who should be nailed first for failing to communicate their position clearly - or is that judging them with the benefit of hindsight....
