The Mansion
Melton Constable Hall, Melton Constable, Norfolk, England was used for the fictional mansion of the Maudsley family, Brandham Hall.
It was mostly built in about 1664-1670, and is considered to be the finest example of the Christopher Wren style of country house.
https://en.wikipedia.org/wiki/Melton_Constable_Hall
https://landedfamilies.blogspot.com/2016/06/219-astley-of-melton-constable-and.html
L.P. Hartley, author of the novel visited a real mansion named Brandenham Hall in 1906, which is probably the inspiration for Brandham Hall. The Brandenham estate once belonged to the Haggard family and H. Rider Haggard was born in a building on the Brandinham estate in 1856.
https://www.literarynorfolk.co.uk/bradenham.htm