Donald Trump’s announcement that he will lift punishing US tariffs on scotch whisky has been overshadowed by a row between rival Scottish party leaders over claiming credit for the decision.

The whisky industry and business leaders were delighted by the US president’s sudden announcement on his Truth Social network on Thursday that he would end the tariffs to mark the visit by King Charles and Queen Camilla.

“The King and Queen got me to do something nobody else was able to do, without hardly even asking!” Trump said.

The Scotch Whisky Association (SWA) estimates the 10% tariff, imposed by Trump last year, has cost producers about £150m in lost sales and led to hundreds of job losses. Shares in Diageo, the drinks giant that produces Johnny Walker, rose sharply on the news.

Graeme Littlejohn, the SWA’s director of strategy and communications, told BBC Radio Scotland the breakthrough was a “demonstration of the soft power of the monarch and what he can bring to the United Kingdom”. It had taken “months and months of work” to get negotiations to this point, he said.

The decision sparked a bitter dispute between the Scottish Labour party, UK government ministers and John Swinney, Scotland’s first minister, over Swinney’s insistence that his meeting with Trump at the White House last September played a significant part in it.

Labour and the Scottish National party, which Swinney leads, are in the final week of a lacklustre Scottish parliament election campaign in which Labour is fighting to prevent the SNP winning a fifth successive term in office.

Swinney was accused of being “shameless” by Scottish Labour’s deputy leader, Jackie Baillie, after he claimed the UK government had done little to raise the tariffs issue with Trump. Swinney said Trump had been unaware of it until they met at the president’s Aberdeenshire golf course last summer.

“As first minister, I have made it my mission to do everything possible to lift US tariffs on our whisky,” Swinney said on Thursday night.

“By meeting the president during his visit to Scotland and by going to Washington, to the Oval Office, we made Scotland’s case. And we used every chance to drive our point home, not least the state banquet hosted by His Majesty the King in London last September.”

Industry sources said UK officials and ministers had been pressing for whisky tariffs to be lifted since the state banquet at Windsor, to which Swinney was invited by the UK government. At the time, the two administrations were in an uneasy alliance to persuade Trump to act.

Douglas Alexander, the UK Labour government’s cabinet minister for Scotland, said trade agreements were the responsibility of the UK government, not Swinney’s devolved administration, and dismissed Swinney’s claims.

“The first minister can hold as many photoshoots and take as many day trips to Washington as he likes – this was delivered after relentless engagement and negotiation with our friends, partners, and allies in the United States,” Alexander said.

Baillie accused the SNP of hypocrisy. She said Stephen Flynn, the SNP’s Westminster leader, had called for Trump’s state visit last year to be cancelled after the president humiliated the Ukrainian leader, Volodymyr Zelenskyy, while an SNP candidate and former advisor to Swinney had called for an end to the monarchy several days ago.

Jack Middleton, the SNP candidate for Aberdeen Central, told a BBC Debate Night election special “the royal family have frankly brought nothing but embarrassment to Scotland and the United Kingdom.”

Baillie said the king’s visit to Washington was clearly instrumental in Trump’s decision. “John Swinney and the SNP’s record is so dismal that they are now trying to claim credit for work they are not responsible for.”

The US is the whisky industry’s largest market, worth about £1bn ($1.2bn) a year, and Scotland’s largest export market overall. Scottish whisky producers also buy about £220m worth of bourbon barrels from Kentucky, an essential component in maturing the raw spirit.

Industry sources said it could take months or years for it to recover the lost business. The tariffs “had led to the gradual erosion of market share versus other whiskies, in a very competitive market”, said one.