The government’s claims that only 28% of farmers will be impacted by the new inheritance tax (IHT) rules is at odds with data from its own environmental department, according to the head of the NFU.

The disagreement comes as the debate over IHT for farmers intensifies.

In her maiden Budget Rachel Reeves outlined plans to remove the agricultural property relief (APR) exemption for IHT from farms valued at over £1m. This was met with immediate backlash from industry experts, rural stakeholders and most importantly British farmers, who are primed to enact protests across the country.

Meeting with Defra sectary, Steve Reed and treasury officials, NFU president Tom Bradshaw demanded the changes be revoked and for discussions to take place between the agricultural sector and Defra to produce a solution to the matter.

On the surface the government introduced the tax to counter wealthy intent on buying up land to avoid paying inheritance tax, with experts such as tax policy writer Dan Neidle supporting the move and criticising the media coverage of the ongoing debate.

However, the true number of farms set to be affected by the change in taxation remains unclear, with treasury figures now being questioned.

Speaking after the budget the chancellor claimed that 72% of British farms would be unaffected, supporting her argument that her government would protect ‘small family farms’. But the NFU argue that the figure will be closer to 66%, with medium-sized family farms, cash poor and rich in just assets, feeling the financial squeeze should the threshold remain at £1m.

The Treasury’s assumption was based on previous claims for APR, but many assets on farmland were claimed under a separate IHT relief scheme, Business Property Relief (BPR), the NFU argues. Under the new regime, these schemes have been merged.

The NFU believes the Treasury has therefore underestimated the value of many UK farms, while Defra’s more recent data provides a clearer picture. This data, compiled when farms registered their value and size after the UK left the EU’s farm payment system, is seen as a more accurate reflection of current farm values.

Mr Bradshaw informed the press that his counterparts at the meeting have agreed to collaborate on finding the “true figure”, but emphasised that farmers felt betrayed by Defra secretary Steve Reed who promised pre-budget that APR would remain unchanged.

He told journalists: “They do not understand the immediate impacts this having to intergenerational farms. Some very, very concerned successful businesses have a parent involved who is in their 80s but the person running the farm is in their 50s. The assets are still in the ownership of the older family member. We have seen some in ill health who will not live seven years to utilise the gifting rules. It is unbelievable the pressure they are putting on the industry. To make this change now, to rip the rug out from under the farming industry, I don’t see how they can justify it.”

The NFU usually advises its members not to protest but Bradshaw advised that “militant” action may be forthcoming following the announcement of a rally at Westminster on November 19 – supported by a petition of over 190000 signatories.

He said: “The outrage from rural communities is like nothing we have ever seen before. They are talking about militant action. We’ve always said, don’t protest, but we can’t say to people don’t do that now. We will be doing our mass lobby for people who have a meeting with a constituency MP but I know others are doing other things.”

The NFU policy chief, Nick von Westenholz, explained: “In a very best-case scenario with spouses using all of their allowances it’s true they can claim up to £3m but in most instances that will not be the case. Not all farm business owners are married. One of the spouses could have other assets which use up the £1m threshold.

“So, it is not a reasonable figure to say that it will be available for most farms. Good policy should be based on the reasonable worst case scenarios rather than best case scenario”.

A government spokesperson said: “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.”