To say that William Gladstone enjoyed reading is like saying Harry Potter is a bit popular among ten-year-olds. The great Victorian prime minister was a bibliophile and polymath of the most extraordinary kind, who was said to have read 20,000 books in his long life.

Some of those treasured books, previously unseen by the public, come up for sale tomorrow, when the private library, which he himself began as a boy, from Gladstone's childhood home is disposed of at auction.

The sale of the private collection from Fasque House in Kincardineshire, the home of the Gladstones in Scotland, is being described as one of the most important book sales in decades. Bids have already been received from private buyers and institutions from all over the world.

There are so many books, up to 5,000, that the auctioneer, Jonathan Taylor, has split the collection into two sales, with the second taking place in October.

Times Archive, 1896: Mr Gladstone reveals the secrets of his library

He bought in his youth the original edition of Scott's earlier novels down to Quentin Durward, which were bound for him while he was a student at Oxford

• Obituary: William Ewart Gladstone

• Mr Gladstone in his library

Although Gladstone's most extensive book collection is housed in the library at St Deiniol's in Hawarden, North Wales, a site of learning he founded formally in 1889, the collection in Fasque dates from his early life and includes important family books.

Among them are Bibles, poetry, literature and a vast range of books on ornithology, military history, botany, exploration and geography. Also included are collections of photographs, plus letters on slavery written in 1830 by Gladstone's Scots-born father, Sir John Gladstone, a successful trader who owned slave plantations in Jamaica and Guyana.

Mr Taylor, of Taylor's Auction Rooms, Montrose, said that there were 450 lots, an estimated 2,000 books, in tomorrow's sale. Interest had been expressed from everyone from the local council to the British Library.

Mr Taylor said: “There are various books that the family have collected over the years, all of them interesting from one angle or another. There are some which are Gladstone's. His father bought Fasque in 1826, when they moved up from Liverpool, and the family grew up there.

“Gladstone started the library, and then his brother Thomas put his books into it, and his nephew John. A lot of the early ones are William's,that he bought when he was at Oxford. From what the family have said, his father said to him, ‘If you want a library at Fasque, go and get it started.' That's how it came about.”

The range of books reveals the erudition of Gladstone, a man so driven and energetic that in his diaries he accounted for every 15 minutes of his day. He spent many hours during his time at Oxford from 1828 to 1831 visiting local booksellers to feed his hunger for knowledge.

Gladstone, who was very fond of Fasque, spent a lot of time there until 1851, when his father died and the estate passed to the oldest son, Thomas. In later life, he returned again.

There are personal diaries and photograph albums relating to the tour to Australasia by Gladstone's sister Mary in the late 1800s, rare in that few photographs were taken in New Zealand at that time.

Also for sale are four volumes of The Roman State from 1815 to 1850 by Luigi Carlo Farini, translated by Gladstone in 1851 and bearing the inscription on the flyleaf: “Sir Thos Gladstone from his affectionate translator”, and valued at £50 to £80.

Along with Christies, Mr Taylor has already helped dispose of the furniture and contents of Fasque. The palatial home has been sold by the Gladstone family and there are plans to convert it into a luxury hotel.

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