* Harry Potter author donates to pro-union campaign
* She compares some nationalists to her Death Eater characters (Changes dateline, adds details, quotes throughout)
By Belinda Goldsmith
LONDON, June 11 (Reuters) - JK Rowling, Britain’s best-selling author and creator of teenage wizard Harry Potter, has donated 1 million pounds ($1.68 million) to the campaign against Scottish independence, saying on Wednesday she believed Scotland was better off staying in the United Kingdom.
Rowling lives in the Scottish capital of Edinburgh where she wrote the first of the Potter series in a local cafe and will be among about four million Scottish residents to decide on Sept. 18 whether to end the 307-year tie to England.
Rowling said she was concerned about the economic impact of going alone, with Scotland’s oil and gas reserves being depleted and an ageing population, becoming the latest in a string of celebrities to wade into the increasingly heated debate.
“The more I have read from a variety of independent and unbiased sources, the more I have come to the conclusion that while independence might give us opportunities - any change brings opportunities - it also carries serious risks,” she wrote on her website.
Rowling said she knew her stance might put her in the firing line of a fringe of aggressive nationalists whom she compared to Death Eaters, followers of Harry Potter villain Lord Voldemort.
“While a few of our fiercer nationalists might like to drive me forcibly over the border after reading this, I’d prefer to stay and contribute to a country that has given me more than I can easily express,” she wrote.
“I just hope with all my heart that we never have cause to look back and feel that we made a historically bad mistake.”
A spokesman for the Better Together campaign confirmed Rowling had donated 1 million pounds to the fight to keep Scotland in the United Kingdom which is the biggest donation yet to the pro-union campaign that is leading in opinion polls.
The largest donation to the team fighting for independence has come from Britain’s biggest lottery winners, Scottish couple Colin and Chris Weir, who have given about 3.5 million pounds from their 2011 winnings of 161 million pounds.
Rowling, who was born in England but has lived in Scotland for 21 years, first went public with her opposition to Scottish independence in 2012 but her statement on Wednesday spelt out her thinking.
She said she believed Scotland was more powerful in global markets as part of the union with England, Wales and Northern Ireland and was concerned about Scotland’s relationship with the rest of the United Kingdom if it broke away.
“If we leave ... there will be no going back. This separation will not be quick and clean: it will take microsurgery to disentangle three centuries of close interdependence, after which we will have to deal with three bitter neighbours,” she wrote.
Other celebrities publicly to oppose independence include singer David Bowie who appealed to Scotland to stay with the United Kingdom at an awards ceremony in February and Scottish comedian Billy Connolly who said it was a time to stay together.
But other big Scottish names are backing independence including James Bond actor Sean Connery, a long-term nationalist who said independence was too good an opportunity to miss.
One major Scottish celebrity, tennis player Andy Murray, has refused to take sides in the debate, although he admitted this week that he did not like Scottish leader Alex Salmond holding up Scotland’s blue and white flag, the Saltire, behind Prime Minister David Cameron when he won Wimbledon last year.
Opinion polls currently suggest Scots are reluctant to break away although support for independence has risen this year.
A TNS poll on Wednesday showed 42 percent of voters opposed independence while 30 percent were in favour and 28 percent undecided. The numbers were unchanged from a month ago. (Editing by Stephen Addison)