As the celebrated neurosurgeon, atheist and campaigner for assisted dying faces his own death, he reflects on what matters most: honesty, humility, serving his patients and building a doll’s house for his grandchildren

I have often cut into the brain and it is something I hate doing.” So begins neurosurgeon Henry Marsh’s 2014 bestseller, Do No Harm: Stories of Life, Death and Brain Surgery, a mixture of memoir and reflection that plunges readers into the world of brain tumours, strokes and head injuries that Marsh has inhabited for 40 years. It is a world in which life is so fragile and uncertain you’d think it would serve as a daily memento mori for anyone working in it. Not so. Recently retired, 71-year-old Marsh has been diagnosed with advanced prostate cancer, and the switch from surgeon to patient, and the prospect of death, has come as a profound shock. And Finally, published this month, is in part a cry of anguish: “My wish to go on living,” he writes, “is as overwhelming as love at first sight.”

But meeting Marsh at his house – an unassuming nineteenth-century semi in Wimbledon, south London – he seems the opposite of lugubrious. With a plummy accent, Harry Potter-ish glasses, and a forehead deeply furrowed by decades spent probing and peering deep into the white jelly of brains, he is welcoming and humorous, and radiates restless energy. We begin our interview in his kitchen, with the Ukrainian family to whom he’s given sanctuary wandering in and out. But it’s not long before he suggests that we walk down his long, lush garden, past his beehives, to his workshop. This looks like a potting shed but is in fact a charmed lair filled with thousands of tools, including three lathes, a radial arm saw, a bandsaw and a spindle moulder. Marsh has always taken pleasure in creating his own staircases, tables, roofs and garden fences. Uninterested in money, he says he’d “far rather make things than buy things”.