I removed the smoke smell by:

1.Thorough hoover inc under seats
2.A/C Deodoriser, basically a small canister set in the footwell and AC left on recirculate. Kills the bacteria inside the AC unit
3.Sprayed 10:1 APC (all purpose cleaner) on all headlining and interior trim and wiped over with damp microfibre
4.APC on interior carpets, agitated and then Wet Vac'ed
5.Wet Vac'ed again but this time with a Autobrite flavoured Carpet Deodoriser
6.Cleaned and conditioned leather with Raceglaze Cleaner and Conditioner.

Sounds like a lot of work but was done over 3hrs. The car was owned by an occasional smoker, so it wasn't that bad compared to some.