The passing of the Beerhouse Act in 1830 enabled Peter McMullen to open his own beerhouse named after William IV in Mill Bridge, Hertford. The passing of the Beerhouse Act acted as a stimulus to common brewing and led to an increase in the number of breweries in Hertford, peaking at eight in Hertford in 1838. In 1966 McMullen's were the sole survivor. In 1860 Peter McMullen passed the business onto his sons Alexander Henry and Osmond Henry who began trading as P. McMullen & Sons. The company expanded during this period and acquired a number of local breweries. As the business grew it moved to Old Cross, Hertford in 1891 and a new brewery was built. The new brewery was designed by William Bradford and is now a grade II listed building. In 1897 the brewery became a limited company, McMullen & Sons Ltd, when it owned 90 pubs. Osmond Henry became Chairman of the new company whilst Alexander Henry retired from the brewery and founded a seed merchant in Hertford.
