I got to use the Arrival facility in LHR when I upgraded from economy to business . The check in agent offered RCC pass but I asked if I could have Arrival facility instead. He said that was fine. I think he was being nice since my travel agent screwed up the ticket.

LHR Arrival Facility was nice and clean compared to crowded RCC. It had shower facility (around 10 - 15 I think) and had nice selection of pastries, juices, and soft drinks.