Keir Starmer has accused Boris Johnson of "laughing at" the sacrifice of Brits during the pandemic.
And speaking to The Scottish Labour Conference, he renewed calls to hit Vladimir Putin with the "strongest sanctions", vowing to "tackle the oligarchs here and go after their money."
Yesterday, the Labour leader urged Boris Johnson to sack Tory co-chair Ben Elliot for his role in links between the Tories and Russian money.
And speaking in Glasgow today he said: "Labour is the party of collective security. Labour is the party of NATO. And Labour stands with the Ukrainian people.
"We are demanding the strongest sanctions against Putin - we must tackle the oligarchs here and go after their money, and while we’re at it, clean up our own politics, once and for all."
Mr Elliot, who co-founded luxury concierge service Quintessentially, has been under the spotlight after it was reported he set up the so-called "advisory group" of party donors, some of whom have links to Putin's regime.
Labour claimed that until recently Quintessentially also promoted the work of its dedicated Moscow office in "providing luxury lifestyle management services to Russia's elite and corporate members" on its website, including helping with the best schools, properties and Russian-speaking nannies.
In 2013 Mr Elliot told the Gentleman's Journal this was "due to the influx in Russian-speaking clients coming into London".
Mr Starmer took aim personally at the Prime Minister over partygate.
"At the height of the pandemic, every British family was touched by worry or tragedy," he said. "Everyone was affected because they followed the rules.
"But, some – and one man in particular - felt that the rules just didn’t apply to him. I refuse to accept that."
He went on: "I refuse to accept the pain and sacrifice of so many British families being cheapened, or laughed at.
"No wonder then that under the Tories, trust in politics is now at an all-time low."
Mr Starmer claimed the reputation of Boris Johnson's administration is so low that "even the Scottish Tories are actually embarrassed by it."
And he accused the government of deliberately "wallowing in cynicism."
He said: ""It wants the public to believe that politics is no longer a force for good. And, of course, they don’t care about the consequences of their actions, including the consequences for the Union.
"It might suit the Tories - as much as it suits the SNP - to keep Scotland stuck on pause in the politics of 2014 forever, but I am calling Boris Johnson out."
Mr Starmer said that under Gordon Brown's premiership, "the lights in Downing Street burned late into the night. Not for parties.
"But because here was a Scottish MP who never rested from the task at hand, restless always to improve the lives, not just of Scots, but of families struggling to pay their bills in every part of Britain."
He added: "Downing Street should be a place where the lights are always on.
"Where no matter the time, work is being done by serious people in the service of our country. "
Quintessentially told the Financial Times yesterday: "The group continues to actively monitor its member base and corporate clients to ensure that it is not servicing any individual or corporate body that is on the sanctions lists that have been issued by the UK, EU and US governments.
"Moreover, it can confirm that it definitively is not engaged with anyone on those lists."
