Everyone wants to make a difference, some take it further than most. “Why did I leave big business to go and work in Africa?” repeats Richard Harvey, with his habitual, ready smile. “If you need to ask the question, you probably won’t understand the answer.” Then he sweeps his hand across the table, wiping the metaphorical slate clean. That’s Harvey in a nutshell: simple in appearance, rather more complex underneath.

He surprised the City last summer by stepping down after 10 years of running Aviva, Britain’s biggest insurer and No 5 in the world. He said he just wanted to take a gap year, working for a development charity. So he swapped his chauffeur-driven BMW and £1m pay package for pick-up trucks and poverty in Malawi and Kenya.

Now he is back and filled to the brim with his experiences in Africa. He wants to devote himself to finding business solutions to the problems afflicting the continent and use his contacts and status as a former FTSE 100 boss to get the corporate community engaged. He is, in other words, a man on a mission.

He’s not naïve, however. “I know, I know,” he says, when I point out that bosses have enough to think about right now. “People are lashed to the mast trying to steer their own ship — ask them for an hour to talk about Africa and they just think, ‘you’ve got to be joking!’ ”

But Birmingham-born Harvey, 58, is a very plausible persuader. Tall and silver-haired, with the looks and charm of a TV presenter, he has a steely streak of pragmatism that served him well melding together businesses such as Norwich Union, Commercial Union and General Accident to create Aviva.

The group failed in 2006 with a £17 billion bid for rival Prudential. Its offer was rejected by the Pru’s board, and Harvey — characteristically — wouldn’t go hostile. Two years later he was gone.

He describes the real reasons for his decision to leave as a “conspiracy of coincidences” — he had been a FTSE boss for 10 years, the company was on a “stable plane”, he had been inspired by his youngest daughter’s gap-year work in Uganda and by his friendship with Tidjane Thiam, the African-born strategy director he recruited for Aviva, now finance director at the Pru.

He also wanted to work with his wife, Kay, who had recently overcome breast cancer, and both have long been committed Christians who feel it is a moral imperative to help thy neighbour.

“And you can’t run a company round the world and think the definition of your neighbour is just the person next door,” says Harvey. Then he wipes that table restlessly again. Harvey, who was an early advocate of offshoring services at Aviva, is a man who finds it hard to sit still.

We are meeting at his Westminster flat behind the new Home Office in London. He has sold his house in Chelsea — but still keeps a home in Gloucestershire. He says his year working with the aid charity Concern Universal has made him think “a bit more about our consumption”.

His time in Africa was spent in the field: carrying out research, teaching in schools, drilling wells, devising schemes for more fuel-efficient cooking devices.

He chose Concern Universal from a beauty parade of organisations that wanted to work with him — FTSE 100 bosses don’t announce their desire to work for charity that often. Harvey liked its community-orientated approach.