The prime minister is involved; so is the U.S. deputy secretary of State. The BBC is changing policies. But Bob Vylan remains steadfast.

I deeply regret that such offensive and deplorable behavior appeared on the BBC,' director-general Tim Davie wrote.

London punk-grime duo Bob Vylan are the subjects of a criminal investigation following their set at Glastonbury. This is the story behind the biggest talking point of this year's festival