Right. But I usually stay near Trafalgar Square and the Piccadilly line is much more convenient for that. (Though I will be taking the Elizabeth line from LHR m

Right. But I usually stay near Trafalgar Square and the Piccadilly line is much more convenient for that. (Though I will be taking the Elizabeth line from LHR my next trip because I'm initially going to Shoreditch. And, yes, Heathrow Express is something of a rip-off which the airport steers you towards.)