There is review level evidence supporting:
Smoking cessation causing a reduction in cost to the NHS. Taylor and Lewis state: “There is evidence that smoking cessation services work. Previous modelling commissioned by NICE has demonstrated that the health gains associated with quitting smoking are significant. Further, cost savings can be substantial” 
1. Taylor M, and Lewis L. An Economic Evaluation of Different Interventions to Promote Tobacco Harm Reduction. Final Report National Institute for Health And Clinical Excellence (NICE).