As long as Russian companies cannot fly into EU (and I guess British) aerial space, never mind landing on the airports located there, any such discussion of “you see, this is a private matter only, there’s nothing the Government could have done about it even if it so wished” is besides the point.
They could have just instructed the Heathrow operators “assign X slots for companies A, B, C and that is that”, the same way they’re telling aviation companies “you cannot fly to Moscow, and that is that”, it is all about political will at the top.