My father, Bernard Gosschalk, who has died aged 91, was one of the small group of white activists who, courageously and at considerable personal cost, resisted the apartheid government of South Africa in the 1950s and 60s. Nelson Mandela recognised the important contribution made by this group to the multiracial society he presided over, and held a reception in July 1994 in their honour.

Bernard was secretary of the Congress of Democrats in Cape Town from 1955 until 1960. He was imprisoned without charge twice in the 1960s and held in solitary confinement. On the second occasion, he was released only because his wife, Ruth (nee Fine), took the government to court and, astonishingly, won. This legal precedent resulted in 500 Africans being subsequently released. The authorities made it clear that, next time around, he would stay in prison for a very long time, and so, reluctantly, the family became political refugees, moving from Bernard’s beloved Cape Town to Manchester in 1966. Ruth was also banned for political activities in Cape Town in the 1960s.

After Ruth’s death in 1994, Bernard met and married Zelda Gordon Fish, a South African journalist. Bernard was a devoted carer, both for Ruth during her long treatment for leukaemia, and for Zelda when she developed Alzheimer’s, and he subsequently wrote a moving and poignant book, Z, Alzheimer’s, A Shared Journey (2009), about living with the disease.

He was born in Port Elizabeth, son of Morris Gosschalk, a businessman, and his wife, Ann. While a student at the University of Cape Town, Bernard interrupted his studies to volunteer for the army and fight against Nazi Germany. An architect and town planner by training and subsequently for 15 years in practice, he later became a lecturer at Manchester University. He was an inspiring tutor and ran some 40 housing courses for more than 1,000 local councillors over a 20-year period. He was also secretary of the North West Housing Centre Trust from 1976 until 1994, active as a board member of housing associations and a strong supporter of Shelter.

Bernard led life to the full: he was a passionate, creative, generous person, full of humility and wisdom, idealism and independence, and, above all, complete integrity. He believed passionately in internationalism; in building bridges, not walls; and in justice for all, not riches for the privileged few. He was a frequent letter writer, both to the BBC and to politicians. He loved to challenge people and encourage them to reconsider their views. As a husband, father and grandfather, he was an inspiring role model.

Zelda died in 2013. Bernard is survived by four children, Marion, Sue, Alan and me, 12 grandchildren and a great-granddaughter.