There is something about either Galleries First or the Concorde Room in T5 having an outside terrace which you can smoke on... not 100% sure though, it's just something I recall seeing in passing... I think it's GF though.

Of course, to access those you need to be flying BA from T5 and be travelling in F (for either) or be a oneworld emerald (for Galleries First).

Reading the post you refer to, it reads to me as though it was written before the ban came in in England on smoking on public places. Prior to that ban, smoking areas were available and the situation was as described - now they aren't. LHR's own information makes that clear: http://tinyurl.com/nbrcv5