Not only is it the earliest standard known to exist from a regiment of cavalry of the line in the British regular army, and has a superb provenance, but it witnessed the last time a British monarch personally led troops into battle - George II at Dettingen, Bavaria, in 1743.
Until now it has descended through the family of the subaltern who carried it in the midst of the action and it has been exhibited in three museums.
The standard, of the 8th (Ligonier's) Regiment of Horse, is the sole known remaining example of one from a British regular cavalry of the line regiment bearing the Arms of its colonel, Major General John (later Field Marshal the Earl) Ligonier.
On June 16, 1743, it was carried by Cornet Henry Richardson, who was first commissioned in the regiment three years earlier. At Dettingen - part of the War of the Austrian Succession (1740-48) - the British were part of the 'Pragmatic Army', fighting alongside Austrian and Hanoverian troops against the French, who had outmanoeuvred them.
The British and their allies found their retreat back to Flanders blocked but repulsed the French attacks with heavy losses and were able to continue safely.
Ligonier's Horse were first stationed on the right wing but were one of three regiments switched to the left to throw back the enemy heavy cavalry. The French tried to capture Ligonier's three standards in total and Cornet Richardson suffered 'seven-and-thirty cuts and shots upon his body and through his clothes, besides many on the shaft of the standard'. He was presented with the standard afterwards to mark his bravery - although by sustaining some of the damage that can be seen today it would have probably been retired anyway.
Richardson remained with Ligonier's for four years after the battle.
The obverse and reverse sides are mounted separately upon a board for display and each side is about 22in high and 21in wide (56 x 53.3cm). In crimson silk damask, it has decoration in gold and silver lace, gold and silver wire embroidery and coloured thread.
The estimate at Thomas Del Mar is £25,000-35,000.