Humza Yousaf and Anas Sarwar have clashed over Labour's green energy plans.
The First Minister hit back at the Scottish Labour leader after he was asked if he welcomed the announcement that a publicly-owned energy company would be headquartered in Scotland if Keir Starmer takes power.
Yousaf accused Sarwar of being "far more style over substance" - but Sarwar branded Yousaf "Mr no style, Mr no substance".
Sarwar was told off by Presiding Officer Alison Johnstone for using nicknames, but he insisted that he was "responding to a criticism the First Minister made of me".
It comes as UK Labour leader Starmer announced that the GB Energy headquarters would be in Scotland earlier this week.
The party has come under criticism recently for saying it would not issue any new oil and gas licences if they win the general election.
Labour also scaled back on its pledge to borrow £28 billion a year for green investment.
When Sarwar asked Yousaf if he welcomed the news about GB energy, the First Minister said he was "delighted Anas Sarwar has been able to clarify Labour's position because Labour have had about five different positions on this and about five different weeks.
"I'm often saying to Anas Sarwar that he is far more style over substance but it is good to hear a little bit of substance from Scottish Labour today."
He also said that people could not trust Labour because it rolled back on its green investment and said it would "squander" Scotland's renewable energy.
Sarwar then said: "This is a serious plan and a serious issue. But sadly, we don't have a serious First Minister, because Humza Yousaf can't bring himself to even welcome these plans."
He said that Labour wanted to make Scotland a leader in renewables, creating 50,000 jobs in the process "but Mr no substance, Mr no style can't support any of them.
"So is the First Minister so blinded by his opposition to a Labour government that he can accept what's good for Scotland?"
Yousaf replied: "Anas Sarwar says you should be thanking London masters for the crumbs off the table.
"Forgive me if I have far more ambition for our country. Then this leader of the Scottish Labour Party."
He also accused Labour of being "prepared to completely abandon every single worker in the northeast" of Scotland.
Sarwar attacked the Scottish Government's record for investing in renewables. He said Labour wants Scotland to be a "world leader" and that the SNP had "16 years to deliver for Scotland, and they failed."
Yousaf said that Labour's plan to ban new oil and gas licences "ignores reality". He said his party believes in a "just transition that means we will not leave a single worker from the north-east on the scrap heap."
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