John Gregory Crace, distant relative of Gregory Gregory (through parents Fredericke Crace and Augusta Gregory), is thought to have decorated the Gold Room. The Crace family were the most important firm of interior decorators working in Britain in the 19th century. They worked for every British monarch from George III to Queen Victoria and on a range of buildings that includes royal palaces, Leeds Town Hall and the Great Exhibition building of 1862. John Gregory Crace worked extensively for the 6th Duke of Devonshire at Devonshire House, London, and Chatsworth, designing a wide range of decorative schemes and furniture. He is also well known for his collaboration with A.W.N. Pugin, with whom he worked on the decoration of the new Palace of Westminster, and the medieval court at the Crystal Palace
A particular pointer is the presence of the elongated quatrefoil flower set with a diamond put in background to the cove and upper panels. This is a Gothic motif and unusual in this setting. Often used by Crace who manufactured a wallpaper based on an original design by A W Pugin, the great Gothic revivalist, it became known as the Crace Diaper.
See: https://harlaxtonmanorarchives.wordpress.com/harlaxton-treasure-trail/crace-diaper/