Nope, unlike a number of other European airports. It's more or less illegal since almost any roof falls foul of the wording of the legislation, with the well known exceptions of prisons, the Houses of Parliament and Simon Cowell's office. There are a few airside smoking locations in the UK, BHD and NCL have them. but they are essentially outdoor passageways bolted on to the side of the building structure. At LGW there is a clear smoking area landside outside the buildings, at LHR you'll find some areas at each end of the bus station. And there is a very discrete spot in CCR were I've spotted the odd illegal smoker of tobacco and other products.