A handwritten manuscript of 29 of Emily Bronte’s poems, with pencil corrections by her sister Charlotte, is going up for auction as part of a collection that has been out of public view for nearly a century, the Guardian has reported.

Arthur Bell Nicholls, the widower of Charlotte, sold the majority of the surviving Brontë manuscripts in 1895. The collectors and brothers Alfred and William Law, who grew up 20 miles from the Brontë family home in Haworth, then acquired some of the family’s heirlooms, including the manuscript of Emily’s poems.

The Law brothers’ library at Honresfield House disappeared from public view when their nephew and heir Alfred Law died in 1939, and was inaccessible even to academics. “In the last 90 years, only one or two (very discreet) scholars have had access to slivers of the material, so essentially, only two people alive have seen any of it,” said a spokesperson for Sotheby’s, which is handling the auction of more than 500 manuscripts, first editions and letters from the Honresfield library in July.

Sotheby’s valued the manuscript of 29 poems by Emily at between £800,000 and £1.2m. “It is the most important manuscript by Emily to come to market in a lifetime, and by far the most significant such manuscript to remain in private hands,” said the auction house. “Almost nothing of Emily’s survived – she essentially wrote Wuthering Heights and then parted the world without a trace. There aren’t even really any letters out there by her, as she had no one to correspond with.”

It is the only surviving handwritten manuscript to feature some of Emily’s most famous poems, including ‘No Coward Soul Is Mine’, ‘The Blue Bell’, and ‘The Old Stoic’, and was mentioned by Charlotte in her 1850 preface to Wuthering Heights, when she noted how she “accidentally lighted on a MS volume of verse in my sister Emily’s handwriting. I looked it over, and something more than surprise seized me – a deep conviction that these were not common effusions, nor at all like poetry women generally write. I thought them condensed and terse, vigorous and genuine. To my ear, they had also a peculiar music – melancholy, and elevating.”

Meanwhile trustees of the Brontë Society are calling on MPs to take action to save the “unique” collection for the nation. Describing the library as “unrivalled in its holdings of northern British literary treasures”, the society has written to all northern MPs and elected mayors warning that the Sotheby’s auctions will see “trophy items” acquired “at prices beyond the reach of British museums and libraries”, with many liable to “disappear into the bank vaults of international private investors”.

As well as her classic novel Wuthering Heights, Emily also published a book of poetry with her sisters Charlotte and Anne titled Poems by Currer, Ellis and Acton Bell. She died in 1848 at the age of 30.