In Diageo’s last full financial year, to June 30, net sales of Guinness dropped 5pc, not helped by poor economic conditions in Nigeria, its second-biggest market after Britain and the location for Guinness’s first brewery outside Ireland and the UK, built in 1963.iageo is breathing new life into the Guinness brand with two new variants in the UK, Dublin Porter and West Indies Porter, which it hopes will quench the thirst of craft beer enthusiasts, who have been driving a small, but encouraging recovery in beer sales.