They will be taking stands alongside regulars Mallett and British and sporting art specialist James Harvey, who are also part of the Stanley Gibbons group of companies. Mr Harvey was recently appointed head of fine art at Dreweatts & Bloomsbury Auctions, another member of the Stanley Gibbons group, while Mallett has an ownership stake in Masterpiece Fairs.
Masterpiece London takes place at the Royal Hospital Chelsea from June 25-July 1 (preview on June 24).
Among the highlights of Baldwin's stock will be this fine pewter example of the enigmatic 1776 Continental Dollar.
Little is known about these coins and even the exact denomination is supposition. There are no records of it in the actions of the Continental Congress and it is unknown who authorised or minted them although they were probably struck in New York City.
The images on the coin were based on the design by Benjamin Franklin for the paper currency that was in issue at the time. The obverse featured a sun shining down on a sundial with the Latin word Fugio (I fly) next to it with the legend Mind Your Business at the bottom.
Franklin, a successful Philadelphian businessman, appears to be suggesting 'look after commerce as time flies'.
The reverse side features 13 linked rings each with the name of one of the original 13 colonies surrounding a sun containing the words American Congress and We Are One.
Acquired at a London auction in 1966, this coin was once the property of the famed collector Olive Lloyd Baker, the last descendant of an old London family. It will be priced at £125,000.