An Irish Tricolour reputedly flown over Dublin during the Easter Rising in 1916, and uniforms worn by the British military leader who suppressed the rebellion, are to be sold at auction next month.

The home-made flag, assembled from panels of green, white and orange cloth, and painted with the slogan "Sinn Fein go deo" (Sinn Féin forever) was reputedly flown over one of the buildings occupied by the Irish Volunteers during the Rising. It was recovered from Dublin Castle Yard, where it had been dumped by British troops along with weapons, equipment and uniforms surrendered by the rebels at the end of the Rising.

The flag is expected to sell for up to €50,000 in a sale of historical memorabilia by Whyte's auctioneers in Dublin on November 8th.

Auctioneer Ian Whyte said the “extremely rare, fully provenanced” flag, of “immense historical importance”, had been recovered and saved for posterity by James Hayes, an accounts clerk in the Royal Irish Constabulary office in the Castle. The flag, which was in the Hayes family for many decades, last changed hands at auction in Dublin in 2007, when it sold for €20,000.

Mr White said the current owner – a private Irish collector – had now decided to sell it. Ironically, given the emblem’s symbolic importance, the Sinn Féin slogan was added carelessly – when the flag was laid out incorrectly – resulting in the colour sequence of the Tricolour appearing as a sequence of orange, white and green panels rather than the other way round.

The auction also includes two uniforms which belonged to Gen Sir John Maxwell, the British army leader who was dispatched to Dublin in April 1916 to deal with the Rising. Maxwell was appointed temporary “military governor” of Ireland. He ruthlessly suppressed the Rising and ordered the execution, by firing squad, of its leaders.

Two of his dress uniforms – as colonel and general of the Black Watch (42nd) Royal Highland Regiment – will go under the hammer as a single lot and are expected to sell for up to €20,000. Whyte’s said the uniforms were being sold by an Irish-American collector who had acquired them in a private transaction some years ago in the United States for an undisclosed sum.

One is a review order uniform with the rank insignia of a general. The second is a levée dress uniform with the rank insignia of a colonel, “accompanied by the appropriate kilt, sporran, plaid, trousers, cross-belt with plate, stockings and kid gaiters”.

Both are stored in a steel trunk engraved with Gen Maxwell’s name and titles.