A set of around 150 original building plans, diagrams, sketches and stone masons’ drawings were rediscovered in the attics of Harlaxton Manor in April 2017. These appear to be actual working plans used during construction of the Manor and show the influence of Gregory Gregory throughout. The few dates which are present suggest these plans relate to the whole period of construction from Salvin in 1830s to Burn in 1850s. There is evidence that they had been discovered in “The Plaster Room” above the original Brewery (kitchen today) in 1980 and then somehow got relocated to another attic and forgotten. Unfortunately the plans are mostly in an extremely fragile and fragmented state. Deterioration has been halted by storage in archival pockets to allow cataloguing and photographing before relocating to a more suitable location such as Lincolnshire Archives.
Catalogue list https://archiveshub.jisc.ac.uk/data/gb3454-hd
Photographs of some of the plans
https://www.flickr.com/photos/harlaxtoncollegelibrary/albums/72157682005421260
Harlaxton Manor Archives 
I had a floor plan blueprint that I used in making fire escape plans. I kept it and gave it to the doctor who owned Harlaxton . Over 200 rooms, many unused or unimproved. I was studying architecture then, and the plans were treasured.