I have just been through this inheritance tax business.
We lived with my elderly uncle who died three years ago. Me and my two brothers were left the farm. As I wanted to pay out my brothers, the valuation was done as a probate one, and was in my opinion very high, and not in our favour, either for tax, or for me buying it.
On the advice of our solicitor we tried to get the inheritance tax reduced by saying it was used for farming. My uncle was retired, but the land was let to another farmer for summer grazing, which we have carried on. This farmer had to send a letter confirming he rented the land for his cattle.
Eventually we did get a reduction in the inheritance tax on the land, but we have just paid out a lot of money as inheritance tax on the house and adjoining barn, which although sitting slap bang in the middle of the field, is not classes as part of the farm - even the barn which we argued held winter hay, was deemed part of the residential dwelling.
So, unless you have a farm with a big acreage, it seems unlikely it would be tax free.
I am pretty certain if we sell the farm, we will get done for capital gains too.