The Federated Farmers of New Zealand have slammed the campaign, accusing Dairy Crest, the owner of Country Life, of "protectionism" and "being underhanded" while describing British butter as "pale and insipid".
Launched last week, the campaign created by Grey London features former Sex Pistol John Lydon raving about the fact that he likes Country Life butter because unlike rival brand Anchor, which is from New Zealand, he thinks it tastes the best.
Radio ads feature Lydon in the countryside asking: "Do I buy Country Life butter because unlike Anchor from New Zealand, they support our great British dairy farmers?
Nah, I buy Country Life 'cos I think it tastes the best".
In a similar vein, the print advert features a newspaper page with the headline reading "Revealed: Anchor Butter comes from New Zealand" with Lydon's head bursting through the page with "So?!! I buy Country Life 'cos I think it tastes the best" underneath.
The campaign was developed after research showed that 39% of Anchor butter consumers mistakenly believed that Anchor is actually British, rather than from New Zealand.
Paul Fraser, marketing director at Dairy Crest, said he was "astounded" at the Federated Farmers of New Zealand's comments and would happily send them some Country Life for a taste test.
Fraser said: "This campaign is simply about getting people to stop and think about where their brands come from and allowing them to make an informed choice."
The Federated Farmers of New Zealand have invited Lyndon to go down under to see for himself the difference free range cows makes to the quality of their butter.
Willy Leferink, Federated Farmers Dairy vice-chairperson, said: "New Zealand butter and dairy products, like our wine, is a taste revelation.
"New Zealand's climate and quality pasture means we are in an agricultural sweet spot. British consumers literally taste freedom when they eat New Zealand butter.
"While I'd like to think of dairy farmers as being the rock stars of the New Zealand economy, I'd be pleased to host that old punk rocker, John Lydon, on my farm.
"Perhaps Mr Lydon could use some of the money he got paid for endorsing the British brand to pay for his flight down under."
Lydon's Country Life endorsement has sparked controversy since the campaign's initial launch in last October, many accusing the former Sex Pistols frontman of selling out.
However, the media attention has meant big gains for Country Life, which reported an 85% jump in sales since signing Lydon as its spokesman, with a 25% year-on-year volume growth.