You are in the UK now so the chance of it being underfloor heating is very slim indeed unless you are in a new build from the last 5 - 10 years or so, even then I would doubt it though.
It is probably a combination of the amount of insulation we put in walls, floors and roof spaces along with the fact you downstairs neighbour or neighbours if there is a basement will be using theirs and obviously heat rises.
I know many people here that live in flats above other people that will never switch their heating on and live comfortably.
It is likely that those radiators are your only heat sources coupled with presumably a gas boiler to serve both the radiators and your hot water taps. There will be some kind of controls for it somewhere though, not all systems with have a thermostat in place. My current house has 3 radiators with no thermostat. It is either on or off or you can set time intervals for it to switch on and off by itself but there is no temperature based control.
In the UK? I doubt it very much. It isn’t beyond possibility but under floor heating really isn’t very prevalent here.