Norfolk is one of the places often mentioned to me as a wheelchair friendly UK holiday destination as many of the places have ground floor access and the terrain is generally fairly flat compared to the hilly Peak District where I am from. My journey to Norfolk was a nightmare (I pass out after twenty minutes in a car from pain) but that’s another story! Overall, Norfolk was a fairly disabled friendly UK destination.
Obviously when asking is a National Trust property like Felbrigg Hall wheelchair accessible there are a few things to factor in. The age of this property and listed status obviously factored into the accessibility of the National Trust hall. The entirety of the ground floor of Felbrigg Hall is wheelchair accessible and this included the shop area where you could buy small nicknacks and National trust memorabilia. The upper floor of the Hall itself was not accessible with a wheelchair but it was rather nice seeing the “virtual tour” of this area from a dedicated room in the ground floor. 
As pictured, the old-fashioned flagon flooring of the kitchen/ pantry area is extremely bumpy although my nerve damage does make me extremely sensitive to these bumps and in agonising pain! One of the main strengths of Felbrigg Hall was their free hire of mobility scooters as this was the only possible way a wheelchair user could have explored the vast 520 acre grounds especially since the terrain tended to verge on the gravelly side. The grounds were beautiful and definitely warranted more time exploring than we had. The paths although gravelled were suitable for lots of different weathers so if you were prepared to brave the rain you could zoom around the gardens easily. We visited in the height of summer and still found the garden area spaced out enough that it never felt crowded or overly touristy. If you have any questions then please feel free to email me on disabledtravelwithgeorgina@gmail.com or have a look on the National Trust website where there are more details of the accessibility of Felbrigg Hall; https://www.nationaltrust.org.uk/felbrigg-hall-gardens-and-estate#Facilities%20and%20access.
