Video: The Scots Star Wars actor at centre of a row over 'Enoch Powell is no racist' claim

The play, written by Clydebank-born writer Chris Hannan examines Powell's prophesy of doom over mass immigration in 1968, infamusly described as the 'rivers of blood' speech.

Mr Powell, the Tory MP who died in 1998 and was a former financial secretary to the Treasury, told an audience that allowing high levels of immigration from Commonwealth countries was “like watching a nation busily engaged in heaping up its own funeral pyre”.

The incendiary speech, in reaction to Labour’s Race Relations Act, had Mr Powell arguing that allowing mass immigration from the Commonwealth was “literally mad” and prophesied doom in the language of the Roman poet Virgil: “Like the Roman, I seem to see the River Tiber foaming with much blood.”

He was sacked from the Conservative Shadow Cabinet after his speech.

Now nearly 50 years on, the speech is still enflaming emotions.

Mr McDiarmid has said that he initially thought Powell was a "horrible racist" but now no longer thinks so.

"He was certainly stirring things up in a way, which we would now describe as incitement because of the impact of its language.

“He was surprised by that impact, but he wasn’t totally naive about it. He wanted to make his mark and knew how to speak to an England that was as divided then as it is now.”

Later asked if he found something to like in Powell, Mr McDiarmid said: "Acting works by empathising with your character. If you fail to do that, the audience simply won't take it seriously and the whole thing will fall apart. So I admire him for sticking to his guns. But at the end of the day you have to ask if what he did advanced the argument in any productive way. I'm not sure it did.

"I suspect the audience may go away thinking he was brave but also naïve - or prejudiced but also honest. I think there are elements of all those aspects to him. But he was a significant character in British life. And - whether you like his arguments or not - the issues he raises are as relevant as they ever were."

But Labour MP Ian Austin said Mr McDiarmid was “wrong to claim he wasn’t a racist. Completely wrong”.

The MP added: “I think Enoch Powell was completely wrong and knew exactly what he was doing.”

Mr Austin pointed out that Mr Powell had not only opposed immigration but also claimed black people in the UK were mistreating white people.

Mr Austin said: “Powell was appealing to the worst racist prejudices, and he knew exactly what he was doing.”

But Mr Hannan has said his upbringing in Scotland was an inspiration for his play.

"I knew I wanted to write about national identity and Powell is a good way of exploring that. But the inspiration was partly my own background in a working-class Irish family in Scotland. There was a huge amount of discrimination as the Irish were often seen as unwanted immigrants. So the Powell speech resonated more widely than you might think," he said.

Mr McDiarmid added: "I think we now have a divided Britain, almost down the middle - as it very much was when Powell made the speech.

"There are the people who have reason to be grateful and happy about multiculturalism and there are other people who are feeling rather dispossessed. And that's something which he put his finger on in 1968 - in fact he lit the blue touch-paper.

"So Chris has written about a divided nation but with Powell there's also a divided personality. He was a romantic nationalist and a passionate person: he felt he had an insight into human nature. In a public sense he had two great ambitions: he wanted to be Viceroy of India and then he wanted to be prime minister. They both came to nothing."

The production was seen last year at the Birmingham Rep and is now being restaged in Edinburgh and London.