A H Baldwin & Sons is looking to expand on past successes, with the Hemisphere Collection of British Gold Sovereigns, which will auction on May 8 in London.

The king preferred his left profile and refused to face the opposite direction to his father - a tradition in the design of gold sovereigns

The sale follows Baldwin's auction of the Bentley Collection of British Gold Sovereigns, which totalled almost £4m ($6.6m) in 2013. The Hemisphere Collection spans 525 years, 15 monarchs and seven mints, and is the first of its kind to track the sovereign since its inception.

"In comparison to The Bentley Collection, The Hemisphere Collection brings together both handmade hammered and machine made milled coinage to give the fullest outline of the sovereign's history, offering collectors of both hammered and milled sovereigns an unprecedented opportunity to celebrate the denomination together," explained director of British coins, Steve Hill.

The rarest and most desirable coin in the collection is the King Edward VIII gold proof sovereign, dated 1937, a remarkable piece that was never circulated due to the king's abdication - his tenure on the throne lasted just 326 days before he abdicated to marry his lover, Wallis Simpson.

The coin is unusual in that Edward VIII faces the same direction as his father, King George V, flouting the tradition started by King Charles II that states monarchs should face in the opposite direction to their predecessor. It is valued at £200,000-300,000 ($333,306-$499,959).

Queen Elizabeth II proof coins were not released to private collectors, making the gold proof an extremely rare find

This estimate is matched by a 1953 Elizabeth II gold proof sovereign, which is considered the most valuable coin issued under the current monarch. The proof was never released to private collectors, and only a scant number were given to institutions to display for the queen's coronation.

The example at auction was part of a set the National Museum of Wales sold with the official permission of the Royal Mint, and will appear at auction for the very first time.

Paul Fraser Collectibles has some stunning rare coins for sale.