Achieving adequate levels of physical activity (PA) is important to maintain health and prevent chronic disease. The costs of inadequate physical activity to the NHS have been estimated at over a billion pounds annually. While socio-demographic characteristics such as age, sex and ethnicity have been reported to be associated with different levels of PA, there is evidence that people's social environments may also be important in encouraging a physically active lifestyle. The objective of this paper is to describe associations between the social environment and physical activity among the poorer communities in an outer London Borough, when other socio-demographic factors are controlled for. A household survey was carried out in six poorer neighbourhoods in Redbridge in 2008 as part of a wider health needs assessment. The questionnaire included questions allowing estimation of levels of physical activity as well as extent of social environment [social network score (SNS) and social support score (SSS)]. A random sample of households was taken and a total of 799 completed responses from over 16 year old were obtained. The association between physical activity and the social environment controlling for socio-demographic characteristics was estimated using a logistic nested model. Higher SNS was significantly associated with younger age, Black ethnicity, higher education level, higher household income and higher levels of PA in bivariate analyses. Higher SSS was positively associated with Indian ethnicity, higher household income and area of residence. In multivariate analyses higher levels of PA were significantly associated with wider social networks and stronger social support, educational level and marital status. Despite its limitations, our findings confirm that the relationship between low physical activity and weak social networks and low social support, observed in general population studies, also occurs in deprived communities in London. The relationship merits further exploration given the limited evidence on the effectiveness of interventions to promote physical activity.