Hannah Ingram-Moore always knew her dad was a good story. A decorated British Army officer from World War II, Tom Moore is charming, droll and confoundingly energetic. Spry doesn’t begin to cover it: At 99, he was mowing the lawn, tending a greenhouse and driving his own car. When he fell and broke his hip 18 months ago, he bought a treadmill to speed up the rehabilitation. “How many 99-year-olds have a treadmill and still drive?” said Ms. Ingram-Moore, as she explained how she hit upon the idea of having Mr. Moore undertake a one-man fund-raising campaign for Britain’s National Health Service. “We were not ignorant of that fact and we will never claim total surprise.” Still, nothing could have prepared her for the media whirlwind that has swept Mr. Moore, in less than six weeks, into a rare altitude of superstardom: prolific fundraiser, chart-topping performer, book writer and all-around national hero — an enduring symbol of British pluck, during a coronavirus pandemic that has confronted the country with its greatest test since the Second World War.