Henderson was instrumental in bringing about the Edinburgh People's Festival Ceilidh in 1951, which placed traditionally performed Scottish folk music on the public stage for the first time as "A Night of Scottish Song". However, the People's Festival, of which it was part, was planned as a left-wing competitor to the Edinburgh Festival and was deeply controversial. At the event, Henderson performed The John Maclean March, to the tune of Scotland the Brave, which glorified John Maclean, a communist and Scottish nationalist hero.