Farmers have threatened to take “militant” action over the so-called tractor tax of imposing inheritance death duties on family farms over £1 million.

The National Farmers’ Union president Tom Bradshaw told how his body could not reasonably ask members to avoid protests over the issue amid growing anger.

He said: “We have got many people, and we do not support this, talking about militant action. That’s the only way they think their voices are going to be heard and I think that just demonstrates the strength of feeling that there is bubbling up around all four corners of the United Kingdom if this change carries on going the way it’s proposed today.”

He added: “We’ve done everything we can in the past to say ‘don’t protest’. Today, I’m not in a position where I can say to people they’ve got no reason to do that.”

Mr Bradshaw met Environment Secretary Steve Reed and Exchequer Secretary to the Treasury James Murray today.

The NFU chief told of discrepancies between the Treasury and the environment department’s figures for the number of farmers who will be impacted by Rachel Reeves’ decision.

Under plans announced in the Budget, inheritance tax will be charged at 20% on farms worth more than £1 million, although the Chancellor has said that in some cases the threshold could in practice be about £3 million.

Mr Bradshaw said: “Defra [The Department for Environment, Food and Rural Affairs] weren’t consulted on this policy change because otherwise it would have identified early on that there were very very different figures that this decision would have been based on.

“We need to get to one version of the truth to begin with, where we’re working from the same foundation to understand what the impact of this will be. It seems at the moment, Treasury and Defra have different figures that they’re working on.”

He added: “I think it is a mistake rather than anything more sinister. I just hope that everyone is able to recognise that and rapidly get to a position where our members don’t have to worry about these unintended consequences.”

Ms Reeves told the BBC’s Sunday With Laura Kuenssberg: “Only a very small number of agricultural properties will be affected, but last year the benefits of agricultural property relief, 40% of the benefit was felt by 7% of the wealthiest landowners.

“I don’t think it is affordable to carry on with a relief like that when our public finances are under so much pressure.”

But the NFU said that many family farms have a high notional asset value, but very low income and liquidity, which means that the vast majority of owners would be unable to meet the inheritance tax charges, without selling assets.

A government spokesman said: “The government’s commitment to our farmers remains steadfast. It’s why we have committed £5 billion to the farming budget over two years – more money than ever for sustainable food production.

“We understand concerns about changes to Agricultural Property Relief and the Defra Secretary of State and Exchequer Secretary to the Treasury met with NFU President Tom Bradshaw today.

“Ministers made clear that the vast majority of those claiming relief will not be affected by these changes. They will be able to pass the family farm down to their children just as previous generations have always done.

“This is a fair and balanced approach that protects the family farm while also fixing the public services that we all rely on. We remain committed to working with the NFU and listening to farmers.”