Orlando Bloom and Sir Ian McKellen in Lord of the Rings (Credit: New Line)

Amazon has been prevented from pursuing certain storylines in its Lord of the Rings series by the Tolkien estate, according to reports.

Tolkien expert Tom Shippey, who has been advising the studio on the hugely ambitious project, said to have a budget of $1 billion over multiple series, revealed the constraints in an interview with German Tolkien fansite Deutsche Tolkien.

Shippey says that the series will be confined solely to Middle Earth's 'Second Age', the period prior to the 'Third Age', which was seen in Peter Jackson's movies, and that the 'First Age' is 'off-limits'.

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“Amazon has a relatively free hand when it comes to adding something [to the Second Age], since… very few details are known about this time span,” Shippey said.

“The Tolkien estate will insist that the main shape of the Second Age is not altered. Sauron invades Eriador, is forced back by a Númenorean expedition, is returns to Númenor. There he corrupts the Númenoreans and seduces them to break the ban of the Valar. All this, the course of history, must remain the same.

View photos J.R.R. Tolkien (Credit: AP Photo) More

“But you can add new characters and ask a lot of questions, like: What has Sauron done in the meantime? Where was he after Morgoth was defeated?

“Theoretically, Amazon can answer these questions by inventing the answers, since Tolkien did not describe it.

“But it must not contradict anything which Tolkien did say. That’s what Amazon has to watch out for. It must be canonical, it is impossible to change the boundaries which Tolkien has created, it is necessary to remain ‘tolkienian’.”

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Game of Thrones writer and producer Bryan Cogman is on board to help make the series, which is likely to be the most expensive TV show ever made.

But the Tolkien estate is notoriously protective of the writer's work.

It recently expressed its disapproval of the biopic of the writer starring Nicholas Hoult, which took place before he had penned his Middle Earth saga.

View photos Nicholas Hoult and Lily Collins in Tolkien (Credit: Fox) More

In a statement, it said: “The family of JRR Tolkien and the Tolkien Estate are aware of the Fox Searchlight motion picture entitled Tolkien that is due for release in May 2019.

“The family and the Estate wish to make clear that they did not approve of, authorise or participate in the making of this film.

“They do not endorse it or its content in any way.”

Christopher Tolkien, the son of J.R.R. Tolkien, who is the literary executor of the estate, told French newspaper Le Monde that managing his father's work amounted to 'intellectual despair', and that numerous requests for participation in dramatising his life had been turned down in the past.

“I could write a book on the idiotic requests I have received,” he said.

He famously hated Jackson's movies too, denouncing them as 'an action movie for people aged 15 to 25'.