How would non British citizens return back home ?

Clearly if planes aren't running at all some carve out would have to be made for such people. If you're in the UK it's not your own home country's Consulate you need to be consulting but rather British immigration authorities (who are probably also closed at this point). I'll say it for the billionth time..."unprecedented circumstances".

https://www.gov.uk/return-home-voluntarily

Some countries (e.g. Australia) are arranging "rescue" types of flights for citizens only to get stranded travelers back to their own countries.

You should not have waited so long to go home. You've had two months or more of warnings about the severity of this particular new virus, lack of vaccines, lack of cures, unknown treatments, to get home/stay home until this crisis passes. Find a way back to your own country, then self-quarantine to protect your family, friends, neighbors, & others from any possibility of virus transmission.