Sir Percy dam Percy's Lass won the Group 3 September Stakes in 1988 (and subsequently died of colic when Sir Percy was a foal. Sir Percy was the last of her offspring) and his damsire Blakeney won the Epsom Derby himself in 1969. Sir Percy was named after Sir Percy Blakeney, the hero of the novel "The Scarlet Pimpernel". In November 2003 Sir Percy was sent as a weanling to the Tattersalls sales. He was bought for 20,000 guineas by Will Edmeades bloodstock, acting on behalf of Anthony Pakenham. Pakenham bought the colt as compensation for losing a National Hunt Horse. Sir
Sir Percy the way and stayed on strongly in the closing stages to finish second, beaten two and a half lengths by George Washington. Sir Percy sustained a pulled muscle in training after the Guineas and his participation in the Derby was in some doubt, with Tregoning considering the less demanding Prix du Jockey Club as an alternative target. On 3 June he started 6/1 third favourite for the 2006 Epsom Derby. The French-trained colt Visindar was the 2/1 favourite, with Horatio Nelson the 11/2 second choice. Sir Percy was held up by Martin Dwyer in the early stages and was only