I can confirm that the Thistle Hotel at Heathrow is brilliant,the outside terrace is just great and of course you can use the facilities,the main bar does not open until 5pm or thereabouts but there is a small shop in reception where you can buy Coffee,tea etc and alcohol and there is food also.Myself and my lad have been here on numerous occasions and the staff are very nice, they are obviously used to aviation enthusiasts and as long as you buy something there is no problem,we are looking forward to the summer where we can spot,take photos and relax.
Martin