The NHS Stop Smoking Clinics rely heavily on giving people advice on using NIcotine Replacement Therapy. Once someone has given up with NRT, and stayed a non- smoker for a month, their success is counted as a statistic.
Research published by the University of Massachusetts, in the United States, in January 2012, suggests that up to a third of those who stop with NRT will start again within a year (despite the fact that they may already be a success statistic).
The NHS expects a hypnotherapist to not count an ex-smoker as a statistic until they have refrained from smoking for a full year.
For info about stopping smoking with hypnotherapy, with testimonials and realistic statistics - see the Effective Hypnosis feature on The Best of Ealing.