JK Rowling, the best-selling author and creator of Harry Potter, has donated £1m to the anti-independence campaign Better Together.
A long-standing supporter and donor to the Labour party and to charity, Rowling's donation is the largest single gift yet given to Better Together, which is run by her friend Alistair Darling, the former Labour chancellor.
In a statement on her website, Rowling, who lives in Edinburgh, said: "I came to the question of independence with an open mind and an awareness of the seriousness of what we are being asked to decide.
"My hesitance at embracing independence has nothing to do with lack of belief in Scotland's remarkable people or its achievements. The simple truth is that Scotland is subject to the same 21st-century pressures as the rest of the world.
"It must compete in the same global markets, defend itself from the same threats and navigate what still feels like a fragile economic recovery. The more I listen to the yes campaign, the more I worry about its minimisation and even denial of risks.
"Whenever the big issues are raised – our heavy reliance on oil revenue if we become independent, what currency we'll use, whether we'll get back into the EU – reasonable questions are drowned out by accusations of 'scaremongering.' Meanwhile, dramatically differing figures and predictions are being slapped in front of us by both campaigns, so that it becomes difficult to know what to believe."
She continued: "If we leave, though, 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.
"I doubt that an independent Scotland will be able to bank on its ex-partners' fond memories of the old relationship once we've left. The rest of the UK will have had no say in the biggest change to the union in centuries, but will suffer the economic consequences."
Rowling made her support for the no campaign public when she was Darling's guest of honour at the no campaign's first fundraising concert, starring the comedian and Labour activist Eddie Izzard, in Edinburgh earlier this year.
Better Together has been warning its supporters and donors for months that it is being outspent by its opponents at Yes Scotland.
Margaret Curran, Labour's shadow Scottish secretary, said this was a "significant and welcome" act by Rowling but claimed that even that £1m left the no campaign poorer than their opponents at Yes Scotland.
"It doesn't take a wizard to work out that Alex Salmond's case for breaking up the UK simply isn't a risk worth taking," Curran said.
"JK Rowling's donation to the Better Together campaign will be put to good use in taking the fight to the nationalists. People cannot be complacent, though. We are up against a campaign supported by big lottery winners. We still need more donations and more support to make sure that people in Scotland say no thanks to separation once and for all."