It was a very civilised protest. The sort of protest you might expect from roughly 10,000 asset-rich, cash-poor millionaire farmers from all over the country. The police officers there just to redirect the traffic. Only the occasional shouted slogans to punctuate proceedings; most people were just happy to be there. “What do we want?” “To not pay inheritance tax on our farms.” It had a ring.

Whitehall has probably never seen so much tweed. Nigel Farage was out there looking like Mr Toad. Flat cap, pristine Barbour jacket, mustard trousers and green wellies. He never can resist a chance to cosplay. Someone might have told him that the streets had been tarmacked a while back. There again, Nige is always willing to piggyback on other people’s grievances. Perhaps he might first like to explain why Brexit has hit farmers so hard.

Also on the march were Kemi Badenoch and Victoria Atkins, the shadow environment secretary, in a migraine-inducing union jack jacket. Kemi stood up to address the crowd. This is your new Defra team, she said, and I commit to repealing the end to agricultural property relief in five years’ time. She may have got a little ahead of herself here. Most farmers don’t have fond memories of the past 14 years. Part of the problem is that the changes to inheritance tax are merely the final straw. Farmers tend to believe they have been screwed over by both the Tories and Labour.

The guest of honour was the newfound celebrity farmer, Jeremy Clarkson. “This is the end of farming,” he declared. Though first he wanted to backtrack a little. He hadn’t – as he had previously told the Times in 2021 – bought his Cotswold farm as a tax avoidance measure after all. He had only said that because he was too embarrassed to say he wanted to have his own pheasant shoot. Mmm. Not entirely sure if I believe you on that one, Jezza.

But like him or not, Clarkson knows how to get a crowd going. This was about farmers’ survival, he said. Next up a swipe at possible trade deals with the US. No one wanted chlorinated chicken. This was a knee in the nuts for farmers. Finally, after an ill-judged attack on the BBC, an appeal to the government for reason. To back down and accept the budget measures had been rushed through with unforeseen consequences. He left the platform to warm applause.

None of which amounted to what Steve Reed, the environment, farming and rural affairs secretary, will look back on as one of his better days. Central London blocked for a protest on your watch is never a good look. And his afternoon was about to get a whole lot worse as he was due to make his first appearance before the Defra select committee.

His first mistake was to arrive early and allow himself to be engaged in conversation with David Barton, a livestock farmer from Gloucestershire. Fair to say, Barton is one of many who think the government has got its maths wrong and that far more farmers will be caught under the new rules than had been predicted. Including Barton himself.

“Are you sure?” said Reed. “You could always give it to your son.” This was to prove to be a consistent theme throughout the afternoon. Reed would start by saying why the new tax measures had been necessary, only to then give suggestions on how the tax could be avoided. It was as if Steve had a split personality. Part cabinet minister, part moonlighting independent financial adviser.

Even so, this cut no ice with Barton. Where was he supposed to live if he gave the farm to his son? Who knows? There must be an outbuilding somewhere. Steve was on a roll. Sensing an opportunity to close the deal and make a sale. “Do you want to buy some life insurance?” he asked. No pressure.

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At which point, things took a surreal turn with the arrival of the Labour MP Barry Gardiner in the corridor. What he was doing there was anyone’s guess. He’s an inner London MP with no farming connections. Not that this stopped Bazza. He went for Barton. “I don’t believe you only earn up to £50,000 on a £5m farm,” he said. Bazza clearly reckoned he knew more about Barton’s business than Barton did.

Barton assured him he did. Now Gardiner got huffy. “Well that’s a very inefficient return on your capital,” he replied. Not wrong, but hardly the point. As Barton went on to observe: “That’s farming for you.”

Luckily for Steve, he got bailed out by an usher telling him the committee was about to start. He dashed in, flanked by two entirely mute Defra officials. Out of the frying pan. The thing is, Reed’s heart just isn’t in the job. He never wanted to be Defra secretary. He represents Streatham and Croydon and has almost no interest in the countryside. He really fancied the justice brief. So he merely goes through the motions. Never really saying anything that suggests engagement. Or deep knowledge. There’s no malice here. He means well. But he’s nobody’s champion.

The committee chair, Alistair Carmichael, got the ball rolling. There had been no plans to limit agricultural property relief in Labour’s manifesto. So what changed? As night follows day, Steve said: “A £22bn black hole.”

Bingo. We were on to a pre-recorded script. The government still wanted farmers to pass on their farms to their children. It just wanted to make it a bit more difficult. People in the countryside cared more about a functioning NHS than farmers. It was just bad luck. In any case, farmers were making a lot of fuss about nothing. The Treasury’s figures were more accurate than his own. In reality, very few people would be affected. And the farmers could afford it. They had the cash. Even if they didn’t know it.

Round about now, you could see Steve’s head beginning to go down. Whatever the truth, the government had lost control of the narrative on this. None of this had been his idea. It had all been dumped on him by the Treasury at the last minute. All over a measly £500m. It would have been better if Rachel Reeves could just back down a bit. Show a bit of flexibility and raise the threshold to £5m. Get the farmers off his back. He was sick of telling the farmers they didn’t know what they were doing. Sick of being a loyal apparatchik.

Back in his office, hope was at hand. Reed switched on the TV to catch Keir Starmer’s press conference from the G20 in Rio. “Should we prepare for nuclear war?” To his amazement, Keir didn’t say no. Bring it on. A first strike from Moscow would give the farmers pause for thought.

• Taking the Lead by John Crace is published by Little, Brown (£18.99). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.