This interview was first published in September 2017, as Ian McDiarmid prepared to portray Enoch Powell in Chris Hannan's play What Shadows. The actor will be reading Powell's 'rivers of blood' speech on BBC Radio 4 on Saturday April 14, to mark its 50th anniversary

When Ian McDiarmid was offered the chance to play Enoch Powell, his thoughts immediately turned to the famous “Rivers of blood” speech, which the MP for Wolverhampton South West presented to a Conservative Association meeting in Birmingham on April 20 1968: “Oh God, I thought, that horrible racist.”

In the speech, Powell warned of uncontrolled immigration from the Commonwealth to the United Kingdom, spoke of seeing “the River Tiber foaming with much blood” and criticised the then-Labour government’s Race Relations Bill, which made it illegal to refuse housing or employment to someone on the grounds of their colour or their race. It caused a political storm and the following day Edward Heath sacked Powell from the shadow cabinet.

But while Powell has become a totem for intolerance, the private man was infinitely more complex and surprising. These paradoxes have been worked into a play, What Shadows, by Chris Hannan, which received a critically admired premiere at Birmingham Rep last year and now returns for runs in Edinburgh and London.