With a focus on an under-studied group of immigrants in the UK, this paper examines Iranian families' language ideologies and practices at home in relation to Persian acquisition and maintenance for their children. Working within a family language policy (FLP) framework, we draw on sociolinguistic data from semi-structured interviews with eighteen mothers to understand how parental beliefs, their everyday language practices and the attempts they make to maintain, improve, or alter their language use will lead to their children's heritage language acquisition and maintenance. The results of the study suggest that the success in heritage language development and maintenance boils down to parental pro heritage language ideologies and their everyday small-scale practices. It was also found that the interrelationship between language and cultural values and a successful FLP was further reinforced by the parents' migration trajectory and proficiency in English as the societal language. This research also showed that the large size of this diaspora in the UK (particularly in London), their close-knit social network, availability of heritage language weekend schools and the possibility of frequent visits to the home country create a conducive situation for the Iranian diaspora to raise their children bilingually.