He is most known for his charity work, his heavy financial support of medical aid programmes, and for housing 40 child refugees fleeing Franco's forces during the Spanish Civil War.

He joined the Spanish Medical Aid Committee (SMAC) when it was first established in 1936, and later travelled to Spain to visit numerous front-line hospitals.

[9] Henderson's Rolls-Royce ambulance, though heavily damaged and covered in bullet holes, survived the war and was shipped back to Britain in September 1938.

The ambulance was then displayed at a conference for officials of the UK Trades Union Congress (TUC), where it was used to raise monetary funds for Spanish medical programmes.

[9] After the collapse of the Spanish Republican forces, Henderson was involved in the evacuation of Quakers and workers from Save the Children at the British built port of Gandia.

[9] Henderson returned to the UK after the Spanish Civil War and continued to use his political position to campaign on behalf of Republican causes.

[10][11] Henderson's pacificist beliefs exempted him from fighting in WWII, instead he served in both the London Fire Brigade, and Bristol, during World War II.