To assess breast-feeding initiation and rates of exclusive breast-feeding for the first 6 months after birth, and to examine social class differences in breast-feeding rates.

First sweep of a longitudinal population-based survey, the Millennium Cohort Study.

Four countries of the UK.

Subjects were 18 125 singletons born over a 12-month period spanning 2000–01. Data were collected by parental interview on the initiation of breast-feeding and exclusivity at 1, 4 and 6 months after birth.

Overall breast-feeding was initiated for 71% of babies, and by 1, 4 and 6 months of age the proportions being exclusively breast-fed were 34%, 3% and 0.3%, respectively. There were clear social class differences and mothers with routine jobs with the least favourable working conditions were more than four times less likely (odds ratio (OR) 0.22, 95% confidence interval (CI) 0.18–0.29) to initiate breast-feeding compared with women in higher managerial and professional occupations. Women in routine jobs were less likely to exclusively breast-feed their infants at 1 month (OR 0.42, 95% CI 0.36–0.50) and 4 months (OR 0.5, 95% CI 0.31–0.77) compared with women in higher managerial and professional occupations.

Clear social class differences in breast-feeding initiation and exclusivity for the first 4 months were apparent in this large UK sample. By 6 months, less than 1% of babies were being exclusively breast-fed. A co-ordinated multi-faceted strategy is required to promote breast-feeding, particularly among lower-income women.