A copy of Shakespeare’s first folio – a book containing 36 of his plays published seven years after his death – has been discovered at a stately home on a Scottish island.

The book, which has languished in the library of Mount Stuart on the Isle of Bute for more than 100 years, was confirmed as genuine by Emma Smith, professor of Shakespeare studies at Oxford University.

Published in 1623, the first folio brought together the majority of Shakespeare’s plays and without it there would be no copies of more than half of them, including Macbeth and The Tempest.

The find brings the total number of known copies to 234 ahead of the 400th anniversary of the playwright’s death on 23 April.

Mount Stuart’s copy belonged to Isaac Reed, a well-connected literary editor working in London in the 18th century, Smith said.

A letter from Reed shows he acquired it in 1786 and further records indicate it was sold after Reed’s death in 1807 to a “JW” for £38.

After this sale there are no public records of the folio and it was not included in Sidney Lee’s 1906 census of first folios.

It was at some point between these two dates that Mount Stuart acquired the book because it is mentioned in a catalogue of the library in 1896.

The Mount Stuart edition is unusual because it was bound in three volumes with many blank pages which would have been used for illustrations.

Smith said: “When we think of Shakespeare we usually think of his plays being performed on stage. But the written word and the first folio is central to our understanding of Shakespeare. I hope this anniversary year encourages people to reread the texts of his work.”

The discovery will form the focal point for a new education programme and will go on display from 7 April at Mount Stuart as part of an exhibition that will run until 30 October.

The head of collections at Mount Stuart, Alice Martin, said: “In terms of literary discoveries, they do not come much bigger than a new first folio, and we are really excited that this has happened on Bute.”