The service sometimes suffers at LHR even with the full cabin crew complement.
I wish they put an extra senior crew member on board, as it's very difficult for a cabin manager to look after F and J on their own. But I do not see this happen, with the lack of crew going on at the moment (which apparently is supposed to go on for a while).
LGW in general work much harder than their brothers and sisters at LHR and that's why the service might not have suffered as much as one would think. When it does, I still think it's the premium service that suffers the most. Which is a real shame.