The authors introduce a simple stochastic model of public opinion formation to explain the support for one (out of two) issue. They show that the joint effect of local (neighbourhood) interaction and a tendency to agree with the opinion held by the majority can explain the creation of large homogeneous areas. They define individual behavioural rules based on simple majority rules. According to the specific rule that is followed by each individual, either contagion on one opinion, or consensus among all individuals, or co-existence of both opinions are obtained.