In 1859, the Royal Mint was presented with two complete silver and gold proof sets of U.S. coins by Professor J.H. Alexander, U.S. commissioner on a joint British/U.S. study on a common decimal currency between the two countries.
Though the proposed shared decimal system never came to pass, the Royal Mint kept the proof sets on display, one set showing the obverse and the other reverse of each coin (that's why the silver quarter in the photo above is blue - that's from decades of toning.)
As related on CoinWeek (scroll down to second article), the Royal Mint recently decided to deaccession one set, and use the proceeds to acquire other items for their collection. Since one set was missing the $3 gold piece, it was resolved to break up and sell the eleven coins of the incomplete set. The Royal Mint sent the coins to PCGS for grading before consigning them to Morton & Eden. The four gold coins are all rated Cameo, with grades from PR64 CAM to PR65+ CAM. The silver coins were rated from PR63 to PR65.
The auction, scheduled for March 6, 2013, is highly anticipated, as the 1859 proof sets did not sell well, and most were melted down in 1860. This auction provides an opportunity to acquire some rare 1859 proofs in excellent condition. The coins are the proof one cent, proof three cent, proof half dime, proof dime, proof quarter, proof half dollar, proof silver dollar, proof gold dollar, proof quarter eagle, proof half eagle, and proof eagle