Additionally, spouses can transfer their nil rate bands to each other tax-free, meaning a widow could protect £1 million from the taxman.

A farm-owning couple would each benefit from an extra £1 million to use towards their farming assets, but this £1 million of farm relief must be used on death. So a farmer leaving everything to their spouse would lose their own £1 million. The surviving spouse would still benefit from their own £1m relief, but as a couple they would not benefit from the full £2m available, costing a family farm £200,000 in tax of £3 million.

Instead, a farmer would be better off leaving £1m of farming assets to their children and the rest to their spouse, who could then use their own £1m relief to reduce the farm’s tax bill. family.

Chris Etherington, of accountancy firm RSM, said: “One of the reasons farm aid existed in the first place was to keep a simple tax for families. These rules assume that people must seek advice in order to benefit from the full tax relief available to them.

He added: “For most people, the standard approach is to create a mirror will and leave everything to their spouse on the first death. But that’s not necessarily the best way to do things right now.”

Farmers have denounced the Chancellor’s decision to include farms and businesses, which previously passed to heirs tax-free, within the inheritance tax net. From 2026, recipients will have to pay 20% tax on agricultural assets worth more than £1 million.

Despite misgivings, Ms Reeves insisted the tax raid was necessary to repair the country’s crumbling public services and restore public finances.

She said on the BBC show: “Last year the benefits of farm property relief – 40 per cent of the benefits were felt by seven per cent of the richest landowners. I don’t think it’s affordable to continue with such relief when our public services are under so much pressure.

“And of course, farmers rely on good public services too, whether that’s our NHS, our roads or our schools. This money will be reinvested in improving our public services and consolidating our public finances.

The Treasury has been contacted for comment.