As Mr Sunak – the third Prime Minister since early September – moves into Number 10, calls from opposition parties for an election to be called grow.
Ian Blackford claimed Mr Sunak is scared of going to the country, with polls suggesting a substantial Labour majority could be returned.
The Prime Minister is said to have ruled out calling an election when he spoke to MPs on Monday.
Mr Blackford said: “Rishi Sunak is running scared of democracy by refusing to hold an election.
“He is feart of voters and too afraid to face their verdict, after the Tories plunged the UK into economic chaos.
“People are paying through their teeth for Tory mistakes as mortgages rise, pensions fall, and inflation soars.
“No-one voted for this – and the Tories have no mandate to impose the devastating cuts they are now planning.
“Rishi Sunak shares the blame for the Tory economic crisis.
“He cannot present himself as the answer to a problem he created as chancellor when he imposed a hard Brexit, slashed universal credit, and raised taxes on everyone else while his own family avoided them.”
Meanwhile, SNP Westminster deputy leader Kirsten Oswald criticised Ms Truss for failing to use her final speech in office to apologise for the economic turmoil that took place during her tenure.
Her short time in No 10 was marred by economic issues, some of which were caused by policy announcements such as unfunded tax cuts.
The Bank of England was forced to step in and buy up Government bonds to steady the economy, while the International Monetary Fund was among the voices from around the world urging a rethink.
Ms Truss U-turned on some of the tax measures, before sacking then chancellor Kwasi Kwarteng and bringing in Jeremy Hunt, who axed the majority of her economic plans.
Ms Oswald said: “It beggars belief that Liz Truss couldn’t bring herself to apologise – or utter a single word of regret – for the catastrophic damage she has done to the UK economy.”
Scottish Tory leader Douglas Ross said Mr Sunak had been “frank and honest” as he addressed the nation before entering No 10 for the first time as Prime Minister, adding that he didn’t “try to sugar coat the fact that tough decisions lie ahead”.
“But the country – like the financial markets – can be reassured that our new Prime Minister is uniquely qualified and will work day and night to steer Scotland and the UK through this period,” Mr Ross added.
“Rishi is a tried and tested leader in turbulent economic times and he made it clear he will approach the current economic challenges with the same compassion that we saw from him during the pandemic.
“What came across loud and clear from his address was that our new Prime Minister is a man of calm authority and integrity who won’t be daunted by the hurdles he faces. Rishi Sunak is a serious leader for serious times.”