The UK position of recognising Guaido is untenable surely. Probably won't stop the Judge denying the appeal though.
The slow selective choking of sovereign countries through sanctions was genocide when Madeline Allbright defended the deaths of children due to US sanctions on Iraq, and it may be genocide now.
What can they do?
Take over the military? They already tried that and it didn't work.
Coup them? The 3 million militia members and loyalist colectivos would almost certainly stop any coup.
Defeat PSUV decisively in elections? I doubt Maduro would let it come to that tbh. He seems dedicated to the cause and would probably prefer becoming a full blown dictator over letting the opposition take over.
They can do what they always do: everything.
Full- spectrum economic and political campaign, sanctions (economic war), toppling sympathetic adjacent governments (Brazil, Bolivia, Argentina), funding of internal saboteurs, overt and covert destabilization.
Venezuela is forced to be in a state of constant war basically, without the shooting.