The writer of the best selling Outlander books, Diana Gabaldon, has revealed she does not know why the successful US TV adapatation of her Scottish-themed romantic time travel books are not yet being shown in the UK.

At an appearance at the Edinburgh International Book Festival today, Gabaldon also said how delighted she was with the casting of the TV version, starring Sam Heughan and Caitriona Balfe as main characters Claire and Jamie.

However rejected rumours that the show, made by Starz in US, with Sony handling broadcasting rights outside the US, was being held back from a UK broadcast by Scotland's independence referendum.

She said Sony were still in negotiations about a UK broadcast.

The first episode was shown on August 9 in the US and had 5m viewers, and the second episode added 25% more audience, the author said.

"There are in fact negotiating with one or more UK TV suppliers," she added.

"Why that deal has not come to a conclusion, I don't know, they have been at it for three months at least," she said.

"There has been talk and rumour and speculation, even though there is no evidence on which to speculate, but the most common rumour is that they are waiting until after the Scottish referendum - but there is no evidence to suggest that is true.

"You can take that for what it's worth."

She said the first two books would likely be a series in itself until the third book in the series, which is larger and more complex.

The author also said she would also like to see her Lord John Grey books become its own TV series.

Ms Gabaldon said that Heughan was perfect for the role of Jamie Fraser.

She said there had been talk of the actor Chris Hemsworth, who stars as Thor in the successful superhero movies of the comic character.

"I am thrilled with the actors, I was thrilled they were unknown because well known actors come with baggage," she said.

"I had a lot of people saying they wanted Chris Hemsworth, and putting aside his nose which is not Jamie Fraser at all, no one would ever be able to look at him without seeing Thor.

"And beside he is Australian, he would not be able to do a Scottish accent.

"I wanted a Scottish actor if humanely possible and Sam is from Dumfries and Galloway."

She confirmed that the Scottish actor Frazer Hines, who she first saw in a kilt in an episode of Dr Who as the character Jamie McCrimmon, which partly inspired Outlander, will appear in the new series as the governor of a prison.

"He is a lovely guy and I am really pleased," she said, "He will be Sir Fletcher Gordon, the governor of Wentworth Prison."

In a lively question and answer session, Ms Gabaldon also said the first image she had for the 9 book series was a man in a kilt.

She said: "I was once asked by a German interviewer: 'Can you tell me, what do you see when you see a man in a kilt?'

"I was really tired and I said, 'I suppose its the idea that you could be up against a wall with him a minute.'"

The last answer reduced the packed main theatre of the festival to gales of laughter.

The latest instalment of the saga, Written In My Own Heart's Blood, is partly set in 1778.

The American network Starz have filmed the first series of Outlander in Scotland.

The £50 million fantasy blockbuster made its global debut in the US and Australia last week, with the maker and entertainment channel Starz announcing a second series after it drew more than five million viewers in the US.

However, there have been no plans announced for the series to be shown on TV in the UK and it is uncertain whether the second series will be shot in Scotland and based at its studios in Cumbernauld.

Ms Gabaldon was in Cumbernauld yesterday at a script reading for the show.

She said the new series will likely begin shooting early next year.