The trolls who insulted JK Rowling over her Better Together support only strengthened the unionist cause

How Scottish do you have to be to hold an opinion on the subject of independence?

Rowling's donation of £1m to the No Campaign is the largest they have so far received (Reuters)

Joanne Rowling still has her magic. The author’s argument for Scotland to stay part of the Union, published yesterday, is twice as long as this column and more than twice as easy to read. It is one of the best written and best argued pieces I have ever come across.

She notes that “when RBS needed to be bailed out, membership of the union saved us from economic catastrophe,” and says she is worried about the economic risks of independence.

She accepts that some will say that this is “poor-spirited”, “because those people take the view ‘I’ll be skint if I want to and Westminster can’t tell me otherwise’. I’m afraid that’s a form of ‘patriotism’ that I will never understand.”

I thought it was telling, though, that she felt she had to start by laying a claim to the right to express a “valid view” on the question. She was “born in the West Country and grew up on the Welsh border”, but her mother was half Scottish.

She has lived in Scotland for 21 years “and plan to remain here for the rest of my life”. She did not need to say that she wrote her first book in an Edinburgh café, and that her entire literary output - the most successful in the world - is a Scottish cultural export. Yet, “I suspect”, she writes, that there is a fringe of nationalists who “might judge me ‘insufficiently Scottish’”.

How Scottish do you have to be to have an opinion on the subject? My mother is half Scottish. I could play football for Scotland. That is, if I could play football to the required standard, I would be entitled to choose to play for the national team, having had a Scottish grandparent.

My father’s family is Scots Irish - the family name comes from Rintoul, a farm in Perthshire. I went to primary school in Scotland. But I live in London and so I don’t have a say in whether the current residents of Scotland change my country for me - “my country” being both the UK and Scotland.

I don’t like it, but I accept it. The right to self-determination has to rest with the people residing in the country at the time of the decision. There is no other way to decide it without, as Rowling says, getting “Death Eaterish” - a reference to the baddies in Harry Potter, the supporters of Lord Voldemort, who worry about the “purity of your lineage”.

Without defining a pure-bred Scot in the way Death Eaters would define a pure-bred wizard, the electorate for the referendum has to be defined by where they live.

The corollary of that is that when someone such as Rowling, who lives in Scotland, expresses her view nationalists have to accept her right to do so. She should not have felt the need to declare: “My allegiance is wholly to Scotland.” Touching as it is to hear of her “gratitude for what this country has given me”, it is beside the point. All that matters is her postcode.

Most nationalists understand this. Kevin Pringle, the Scottish National Party’s spokesman, wrote of his “respect” for her and said that he agreed on the point that, if the Scottish people voted for independence, it should be a “resounding success”.

But there are also nationalists who might as well be the paid agents of Alistair Darling, Gordon Brown and me. They make fools of themselves on the internet by abusing people with whom they disagree. Yesterday they were out in force, calling Rowling names, and possibly - I lacked the inclination to search all the web forums - calling for a national boycott of her works. They may even have demanded a remake of the entire filmic oeuvre, with Cho Chang - Harry’s love interest who is played in the films by the Scottish Katie Leung - as the hero.

On second thoughts, that may be a little too imaginative for the nationalist trolls. They reacted badly when David Bowie and Barack Obama said from outside Scotland that they don’t want the Union to break up. They predicted that their fellow Scots would respond to being told what to do by outsiders by becoming more determined to do the opposite.

But they react with just as much priggishness when someone almost as famous, who happens to live in Scotland, says the same thing. Throughout it all, however, the Scottish people, as measured by opinion polls, remain stubbornly unmoved. The ‘No’ vote is still set to prevail.

Some unionists yesterday said they regretted Rowling’s failure to set out the positive case for preserving the Union. Well, I don’t agree with that. She is Scottish, isn’t she?

We Scots are suspicious of too much sunny optimism. Give us the negatives. And yesterday, the nationalists who abused Rowling gave us the biggest negative argument against independence of all.