U.K. government-bond futures often move sharply in the 24 hours before sensitive economic reports are released, an analysis of trading data shows, a phenomenon that suggests some investors may be trading with knowledge of official statistics before they are made public.

The analysis highlights Britain’s unusual practices in the handling of market-moving data: Over a hundred people, from Prime Minister Theresa May to dozens of policy advisers and press officers, can get to see some of the figures a day before they come out....