Can you book tickets for an airport lounge for Heathrow Terminal 5?
Terminal 5 isn’t open yet, but when it does open it will be totally occupied by British Airways. You might want to call the closest British Airways reservations office where you live if they offer day passes as they have indicated on their website that only those who hold First or Business Class tickets have access to their lounges. Many airlines such as BA’s partner American Airlines offer day passes for as low as US$50.