McMullen's - or Macs, as it's informally known - has been brewing beer and running pubs since 1827, when Peter McMullen started it. Still based in Hertford, it now has close to a hundred pubs across Hertfordshire and beyond, and brews under the McMullen's Heritage Beers and Rivertown Brewer names.
McMullen's brew at The Hertford Brewery on Old Cross, coming up on two centuries in business. You'll find their two ranges, Mac's Heritage and Rivertown, bottled, in kegs and in boxes.