According to the ONS.
(In Ken Livingstone's case, it appears to be three children in five).
John Woodcock MP Quits Labour Party
4 hours ago
"Things fall apart, the centre cannot hold" - W.B. Yeats. "We're doomed !" - Private Frazer. "Like scrolling through a decade's worth of Daily Mail editorials in 20 minutes" - TheLoonyFromCatford