"He's not mature enough," said Dr Turnovah Newleaf, a biologist at Sussex University. "Metamorphosis into a hot-air balloon is part of the life-cycle of the Dimblebys. But David hasn't reached that stage yet."
His father Richard Dimbleby did his best work after the change, she added. "He used to float above Royal Weddings emitting a sonorous, incomprehensible rumble. It was very soothing."
Dr Phil McCracken, a Glasgow psychiatrist, said: "Close study by scientists resulted in the discovery of Dimbleby Waves. These led to a breakthrough in the treatment of mental disorders, when a machine was invented that could create the waves electronically."
Dimbleby Waves make humans feel secure, said Dr McCracken. "They bypass the bullshit deflectors in our brains. So hospitals use the machines to pacify disturbed patients who believe Britain is run by psychopaths."
Although David has not yet metamorphosed, the change is inevitable, said Dr Newleaf. "You might as well try to stop a caterpillar becoming a butterfly as a Dimbleby turning into a hot-air balloon.
"It's his destiny."