Ms Reeves said that in some cases – where other inheritance tax allowances also apply – the APR threshold could in practice be around £3m, meaning she was only targeting than the richest landowners.

But farming unions in Wales dispute this claim, saying many small family farms will be affected by the changes.

Mr Jones said: “The announced changes not only pose a threat to our family farming structure and agricultural sector, but also to our country’s food security.”

Bernard Llewellyn, a Carmarthenshire farmer, said another effect of the change could be that land sold to pay taxes would be “taken over by companies across the border” to plant trees and “mitigate their carbon emissions”.

It would replace “land used by a young farming family to produce the food this country desperately needs,” he said.

Kate Miles, director of the DPJ Foundation, an agricultural mental health charity, said the organization had been contacted by farmers who were deeply concerned about the situation.

“We’re seeing this level of fear and worry and outrage across the country… a very powerful swirl of emotions that has serious mental health consequences,” she said.