English: Union Flag flown from HMS Minotaur during the Battle of Trafalgar (21 October 1805) and now in the National Maritime Museum (ZBA6946), part of the Royal Museums Greenwich. The flag is made from wool bunting, and – as is common for handmade flags – has been made incorrectly, with the arms of the saltires not aligning with one another in the proper way. Although the Union was typically only flown as a jack by British warships in port, the Vice-admiral of the White, Horatio Nelson, 1st Viscount Nelson had ordered on 10 October 1805:

When in presence of the Enemy, all the ships under my command are to bear White Colours and a Union Jack is to be suspended from the foretopgallant stay.

This flag was, reputedly, the flag flown from this position by the 74-gun third-rate ship of the line HMS Minotaur during the Battle of Trafalgar eleven days later. After this crushing British victory and the death-in-action of the national hero Nelson, the Minotaur’s Master's Mate Stephen Hilton (1787–1872) was awarded this flag together with an Austrian ensign (National Maritime Musuem, ZBA6945) from the 80-gun Neptuno, a Montañes-class ship of the line of the Spanish Navy which the Minotaur captured during the battle. In 1839, the by-then Commander Hilton settled at "Trafalgar House" in Selling, Kent. In 1872, Cdr Hilton was buried in the yard of St Mary's, the parish church at Selling. In the 1930s, Hilton's family, who had retained the flag, donated it to the church, were it hung until efforts to sell both of the Hilton/St Mary's flags began in 2009. The possibility that this flag would be sold into private hands was ended after 2011; the National Maritime Museum agreed to buy both flags. After restoration, and in time for Trafalgar Day 2015, the flag of Minotaur was put on display in the "Nelson, Navy, Nation" gallery alongside Nelson's own uniform worn during the battle. The Minotaur, captained by Charles John Moore Mansfield, had helped defend the Victory during the battle, for which Mansfield was decorated with a medal ([1], [2], [3]). The flag is 2265 mm x 3110 mm (RMG, after restoration), having previously measured 2240mm x 2860mm (Flag Institute).
See: Royal Museums Greenwich website catalogue record, Flag Institute, The Guardian, Royal Maritime Museum curatorial blog, Culture24