As a Liberal MP he supported Irish Home Rule, trade unions, free trade and welfare reforms. Leading up to the First World War he argued that Britain should adopt a more sympathetic approach towards Germany, including naval disarmament. When war did break out, Brunner was resolute in the opinion that it should be fought and won. In addition to the production of alkali, his factories were making other chemicals for use as explosives. He also built a new factory to purify trinitrotoluene.