Lawyer who disclosed clients confidential information is liable for damages

The lawyer who catapulted a promising but obscure new crime writer into the bestseller lists by revealing the author's true identity as JK Rowling, has been fined £1,000 for breach of confidentiality.

The Solicitors Regulation Authority has also issued a written rebuke to Christopher Gossage, of Russells solicitors, who confided to his wife's best friend that Robert Galbraith, author of The Cuckoo's Calling, was really one of the most famous and wealthy authors in the world.

Gossage said he believed he was speaking "in confidence to someone he trusted implicitly", but the story subsequently appeared in the Sunday Times, to the dismay and rage of the author of the Harry Potter books.

The publisher of The Cuckoo's Calling, Little Brown – which also published Rowling's first adult novel, The Casual Vacancy – organised hasty reprints as the book, which up to that point had sold 1,500 copies in three months, shot 5,000 places to the top of the Amazon bestseller lists. In the week after the story broke it sold almost 18,000 copies.

Rowling was furious, however, and even more so when she discovered the source of the leak was her own solicitors.

"To say I am disappointed is an understatement," she said at the time. "A tiny number of people knew my pseudonym and it has not been pleasant to wonder for days how a woman whom I had never heard of prior to Sunday night could have found out something that many of my oldest friends did not know."

Writing on her alter ego's website, Rowling explained: "I was yearning to go back to the beginning of a writing career in this new genre, to work without hype or expectation and to receive totally unvarnished feedback. It was a fantastic experience and I only wish it could have gone on a little longer."

Inevitably there were suspicions that the whole affair was a marketing stunt, but in fact the book had been sent as the work of the unknown Galbraith to several publishers. Orion was one of the few honest enough to admit they were kicking themselves, having seen the manuscript and turned it down.

Rowling's solicitors made it clear that the revelation came from them, not the author.

"We, Russells solicitors, apologise unreservedly for the disclosure caused by one of our partners, Chris Gossage, in revealing to his wife's best friend, Judith Callegari, during a private conversation, that the true identity of Robert Galbraith was in fact JK Rowling.

"Whilst accepting his own culpability, the disclosure was made in confidence to someone he trusted implicitly. On becoming aware of the circumstances, we immediately notified JK Rowling's agent. We can confirm that this leak was not part of any marketing plan and that neither JK Rowling, her agent nor publishers were in any way involved."

Rowling sued both Gossage and Callegari and received a fulsome apology and her costs, and the firm paid undisclosed substantial damages to the Soldiers Charity. Rowling also donated royalties from the book to the charity, explaining that they had helped with the research for the book's ex-army hero, Cormoran Strike.

A new Cormoran Strike thriller is due out in 2014, again listed as authored by the considerably less obscure and even more promising Robert Galbraith.