Mark Sedwill: UK's top civil servant takes a hard line on leaks

Former ambassador to Afghanistan has spent much of his career on security issues

Sir Mark Sedwill suddenly became Britain's most powerful civil servant last autumn, after it became clear that Sir Jeremy Heywood was terminally ill. He took the job without having to go through a formal interview process.

Already the country's national security adviser, he had been deputising for Heywood and, having worked with Theresa May for several years, the 54-year-old was someone the notoriously reticent prime minister felt she could trust.