Astonished Joseph Lathey was told he must hand over his bottle of medium-hot condiment because it contained processed vegetables.
For good measure, the 27-year-old was also told he could not pass with the selection of samosas, flatbreads and various spices he was carrying from a shopping trip to the Rock.
He went back into Gibraltar and sold them all cheap, he says.
Mr Lathey, who lives just across the border in La Línea de la Concepción, said he showed the guard on duty the contents of this bag and was shocked at what happened next.
"Normally they just take a glance and wave you through," he told the Pen News agency. "But this time he casually started going through things and picking stuff up. He seemed a bit confused, which I was a bit taken aback by because that never happens.
"So then he asked me to step aside and he took me over to the guys who usually check the tobacco and the alcohol."
A guard rifled through his bag, pulling items out and reading the back of labels.
"He just started pulling stuff out and said ‘no, no, no, no… but you can have these two things,’ and pulled out two bags of spice that I had and said ‘that’s the only things that you can keep’," Mr Lathey said.
The disgruntled Brit, who had lived in Spain since he was a child, estimates that he was only able to keep £6 worth of his £43 shop.
Instead of handing the rest over, he immediately put ad advert on Facebook and sold it for £20.
Mr Lathey said: “The border police wanted to take the samosas, because they said it had processed vegetables in it.
"There was a bag of cloves, chilli powder, some teriyaki rib rub or something like that that, and the flatbread.
"The Peri-Peri Nando’s sauce was in there, too. It had onion puree on the ingredients and that’s one of the things they said to me: ‘look, it’s got processed vegetables on it, you can’t have it'."
In perhaps the cruellest blow, the Brit revealed he has never actually tried Nando's Peri-Peri sauce.
"I was really looking forward to trying it," he said.
Mr Lathey, who wanted Britain to remain in the European Union, was under the impression that the new rules only prohibited meat and dairy.
But, despite being convinced that the border guards were unsure of the rules themselves, he felt powerless to question their decisions when all the legal documentation was in Spanish.
"When it comes to the border police, you can’t really argue with them," he said. "If they tell you no, then that’s it, you’re not going to get over the border with it, unless you’ve got a lawyer with you – how am I supposed to argue my case?
"All the documentation they had was in Spanish. I’m fairly fluent in Spanish, I’ve been here for about 20 years… but I’m not used to reading legal jargon from a document written by the Andalusian government. It’s very difficult for me to read and understand at a glance.”
Mr Lathey continued: "The customs officer clearly didn’t know any of these laws off by heart, he was having to reference the papers he had, and he seemed as confused by the legal jargon as I was."
And if the rules are that strict, Mr Lathey expects it will lead to a surge in smuggling.
He said: "Obviously, we can buy everything that we need in Spain, there’s no problem there. The thing is that nice things that we want – your Cadbury’s chocolate and your digestive biscuits… all that kind of stuff – you can only get in Gibraltar.
"What that will mean going forward: I can guarantee you that everyone is going to carry on bringing those things through, they’re just going to find imaginative ways of doing it."
An advisory note from the Gibraltar government warns that all meat and milk will be unable to enter the EU from the peninsula but makes no mention of processed vegetables.
The incident comes just the week after border officials in the Netherlands took ham sandwiches off a lorry driver arriving from the UK. “Welcome to Brexit, Sir,” they told him.