Game of Thrones author George RR Martin has admitted that the HBO series is catching up fast with his novels.

George RR Martin has two books left in his series A Song of Ice and Fire and he said he is writing "as fast as I can write".

The next TV season will be based on a published book and the following two will, in theory, have to wait until he completes the remaining two books.

On Tuesday (Aug 12) he told the Edinburgh international book festival: "They've certainly caught up to me, They are writing 60-page screenplays and I'm writing 1,300-page books.

"There is no doubt the show is moving very, very fast. But whether I'm concerned or not concerned makes no difference. I can only write one word at a time, one sentence at a time, one book at a time.

"I'm writing the books as fast as I can write the books and the show is moving along – we'll see what happens, but it's almost out of my hands so I can't worry about it. I just have to worry about telling the stories as best I can."