If you have access to the Plaza Premium lounges, and just want a bite to eat, the T4 arrivals lounge serves a better-than-expected bit of grub. Prawn cocktail, a small portion of fish and chips and a quite yummy chocolate dessert washed down with a liquid or two of your choice. I've done this quite a few times now when overnighting at the Hilton Garden Inn: 482 or 490 bus from T5 to T4 takes 10 minutes. Plaza arrivals lounge. 490 bus from T4 to Hatton Cross takes 10 more minutes.