Britain’s PM race rocked by Dark Horse candidate Penny Mordaunt

LONDON—The unpredictable contest to find a new British prime minister has produced a dark horse.

Penny Mordaunt, little known outside Conservative Party circles, emerges as the biggest threat to former Chancellor of the Exchequer Rishi Sunak’s campaign to take over as party leader. Considered a long shot just days ago, she became favorite in Britain’s betting houses on Wednesday after several polls showed her leading popularity polls among grassroots Conservative members.