"I suspect we're not the only family in the country that likes to have a friendly row on Christmas Day," admits Jim Al-Khalili, sitting in his office in the physics department at the University of Surrey. "I guarantee we will have the usual Al-Khalili religion debate. My wife gets very frustrated about it. It's the same old argument every year."

But this year might be a little more fraught than most. Mr Khalili's mother is still a devout, church-going Christian but, next week, her 40-year-old son will become the next president of the British Humanist Association, the ever-expanding organisation for, in its own words, "people who seek to live good lives without religious or superstitious beliefs".

"She felt somewhat disappointed that I had taken on this role," he admits. "I said: 'You shouldn't be. You shouldn't be any more disappointed than I am that you go to church every Sunday.'"

Mr Khalili, who grew up in Iraq with his Christian mother and his "bordering on agnostic Muslim" father, is a theoretical physicist and also presents The Life Scientific on Radio 4.