UK / London / Airports / LHR
I'm so pleased this forum was given the go-ahead...
Anyway, I wanted to flag this up as there's a widespread view to the contrary that Heathrow is completely non-smoking airside.
It isn't. T4 has a smoking facility which is technically a confined outdoor area. Turn left after Security towards the Pret a Manger, the children's play area and the QR Lounge. The smoking area is down a couple of flights of stairs (there is an escalator heading up) and through a couple of sets of doors.
There is one of those smiley face machines as you enter and exit. I always make a point of hammering the "very happy" button several times in the hope that HAL will eventually see fit to find room for a similar facility in T5...