Moore broke through the square, but his horse was killed under him leaving the lieutenant trapped with only a broken sword.
The Victoria Cross citation from the time explains: “Lt Moore speedily extricated himself and attempted with his broken sword to force his way through the press. But he would assuredly have lost his life had not the gallant young Lt Malcolmson, observing his peril, fought his way to his dismounted comrade through a crowd of enemies, to his rescue, and giving him his stirrup, safely carried him through everything out of the throng.
“The thoughtfulness for others, cool determination, devoted courage and ready activity shown in extreme danger by this young officer, Lt Malcolmson, appear to have been most admirable, and to be worthy of the highest honour.”
Both Moore and Malcolmson were awarded the Victoria Cross, which had only been inaugurated a year earlier.
Mr Cooper said: “Cavalry breaking a square like that didn’t happen very often and it’s an impressive feat of arms. The charge broke the square, the cavalry poured in and it ended the battle.”
The donation is all the more impressive because it contains dozens of items of Malcolmson’s personal kit and the ceremonial uniform he wore for the portrait by Louis William Desanges.
The donor, who has declined to be named, is a direct descendent and has been in charge of the family heirlooms for the past 30 years. The medals have been in a bank for safe-keeping while the other items have been kept in boxes.
She told the Telegraph: “It struck me that they are amazing items but they are stuck in a box or in a bank. No one was able to see them or take pride in them. It was an asset that wasn’t bringing in any money and I was having to pay insurance.
“I felt that all the items should stay together and I have thought about it for 30 years and I have finally got around to making a decision.”
Malcolmson, who was born in Inverness, later fought during the Indian Mutiny and eventually rose to the rank of captain. He died in 1902.