I listened to the exceptionally well-informed podcast by John Goodall and Clive Aslet about Castle Howard (link on Spotify below). 

It comes in two parts.  The first is about the early history of the house and the third Earl of Carlisle’s motivation in building it.  He was, as John Goodall correctly points out, highly ambitious, a member of the Kit-Cat Club and had travelled to Rome, writing detailed notes about his time there.  Vanbrugh was the same generation, a successful playwright.  Carlisle fell out with William Talman, the leading architect of the time, who over-charged for his services.  So, he asked Vanbrugh to come up with designs.  Sketches survive.

The second part is about the recent and very successful renovation of the Tapestry Drawing Room by Francis Terry: an imaginative re-invention, equivalent to what George Howard did in recreating the dome after the fire in November 1940 (not 1944).

The question is raised at the end as to whether the National Trust should recreate Clandon.  After all, the Russians recreated the palaces outside Leningrad with the utmost care after the Second World War.  And was Clandon not insured ?