BackgroundLife expectancy is 10–20 years lower among people with a severe mental health disorder. Most of these early deaths are due to chronic conditions, including cardiovascular and respiratory diseases. Smoking is a major risk factor for these conditions and introducing smokefree policies has been recommended to mental health service providers in England by the National Institute for Health and Care Excellence (NICE), in their Public Health Guideline 48: Smoking: acute, maternity and mental health services. This paper reports a process evaluation of introducing these policy recommendations, which were updated in 2013.MethodProcess data were collected through semi-structured interviews with staff (n = 51), members of partnering organisations (n = 5), service users (n = 7) and carers (n = 2) between November 2016 – April 2017. Normalization Process Theory (NPT) was used to design the data collection tools and analyse the data. A framework approach was taken with the analysis, using the four concepts of NPT: coherence, cognitive participation, collective action and reflexive monitoring.ResultsThe policy made sense to some staff, patients and carers (coherence) who ‘bought-into’ the idea (cognitive participation) but other participants disagreed. Although smokefree policies were operationalised (collective action), sometimes they were opposed. Progress was made, especially in some units, but continued to be resisted in others. Informal appraisal of progress (reflexive monitoring) presented a varied picture.ConclusionSome progress has been made in terms of changing an entrenched, smoking culture into one that is smokefree on Trust sites across the region. Perseverance and resourcing over the long-term is required to establish a non-smoking culture in on-site provision of mental health services.