Even so, it's disappointing that a measure can't be devised to distinguish between long-held family farms and recent purchases for tax avoidance.
And some "family farms" are big businesses, and you'd need some mechanism to prevent a "family" inheriting the farm then immediately selling it (or just the farmhouse, often the most valuable part of the estate).
There are farmers whose children aren't interested or have chosen other careers (a 79 year old farmer recently sold off his prize herd of Lincoln Red cattle for this reason).
I guess that in many cases, like the landed gentry had to sell works of art to pay death duties on stately homes, the tax could be paid by selling off (or mortgaging) part of the land.
Protecting tenant farmer families is another issue.