Arguments against increasing tax on cigarettes
Smokers already pay a lot of tax £7bill. Also they do not cost the government much because they die early and save pension and health care spending
Demand is very inelastic and therefore increasing price will only cause a small fall in demand
Higher taxes will increase inequality because the poor will pay a higher % of tax than the rich who are more likely to have given up (However the government can use other taxes to reduce inequality if it is concerned about this)
Higher taxes will encourage people to smuggle illegal cigarettes and avoid paying the tax.
You could argue that smokers already pay the social cost of smoking given the high level of current tax. Therefore the best argument for increasing taxes is the normative judgement that smoking is bad for people and the government should intervene to reduce demand.