JK Rowling has sparked controversy after questioning a claim that there are no traces of anti-English prejudice within the SNP.

The Harry Potter author, who donated £1 million to the Better Together campaign ahead of the referendum, responded to Herald columnist Iain Macwhirter who described the SNP as "a civic nationalist pro-immigrant party" and said "any trace of ethnic nationalism, and anti-English sentiment, was expunged from the party in the 1970s."

She said it had been "quite a claim" and asked how many English people who had moved to Scotland had been polled to back up the assertion.

Ms Rowling added that she had friends who were SNP supporters and respected those whose allegiances to the party were based on a desire for self-determination, but continued to suggest she was sceptical of total non-existence of anti-English prejudice in the SNP.

She wrote: "I have issue with any non-X person declaring 'there is no anti-X prejudice'."

The writers accused each other of failing to come up with evidence to support their positions in an exchange on Twitter.

In a message to Ms Rowling, Mr Macwhirter said: "making unsubstantiated and unjustified claims about racism and ethnic nationalism in SNP is hugely unhelpful in this debate."

It is the latest online row involving Ms Rowling, an English-born Labour supporter who has lived in Edinburgh since the 1990s and was a repeat victim of abuse in the run-up to the referendum.

The SNP responded by saying it had many people originally from England among its supporters. Several of its elected politicians were born south of the border, including health secretary Shona Robison, former education secretary Mike Russell and veteran MSP Christine Grahame. Meanwhile, Nicola Sturgeon has spoken frequently about her family's roots in Sunderland.

SNP backbencher Nigel Don, who was born in Sutton, said: "Throughout the recent general election campaign the First Minister made clear she wanted to extend a hand of friendship to England and the rest of the UK, making the case for progressive change across the country.

"It was also encouraging to see over 44,000 people south of the border sign a petition for the north of England to become a part of Scotland - that is a sure sign of the warmth that exists between the two nations. There is no place for personal abuse of any kind in politics on any side of the debate and the SNP has been crystal clear that such abuse must stop, full stop."

Adam Tomkins, an academic and prominent No voter last year who represented the Conservatives on the Smith Commission, entered the debate by claiming he had never experienced anti-English sentiment from the SNP.

SNP MP for Na h-Eileanan an Iar Angus MacNeill then intervened by asking Ms Rowling to prove there is no anti-English, Scottish or Welsh feeling among the Tories, Labour or UKIP.

Ms Rowling responded sarcastically by writing: "The birthday of my life is come, as Christina Rossetti once said. Angus, I have dreamed of this day!"

She then replied: "Angus, that's my point. Proving a negative isn't very easy to do. Thanks for your contribution, though. Very valuable."