Labour would instead fund the levy “by taxing the incomes of landlords, and those who buy and sell large quantities of financial assets, stocks and shares”, he said.

But at the time the rise  was announced, Treasury sources argued that raising the required £12 billion for the national health and social care levy could only be achieved by increasing either NICs or income tax.

Challenged on whether Labour’s alternative plans would raise the £12 billion required, Ms Reeves said: “Well, there’s lots of papers out there from different organisations that show you could do exactly that.

“We will set out our plans ahead of a general election, but it’s not right just to ask those people who go out to work for a living to pay higher taxes, especially at a time when the prices of everything are going up.”

On Thursday, a leading think tank said Rishi Sunak should solve the cost of living crisis by giving all households who pay a basic rate of tax a one-off cheque for £300.

Rather than constructing a complex support package for families struggling with the rising cost of energy bills and other goods, the Social Market Foundation said the Chancellor should “just write millions of cheques”.

A Treasury source said no final decisions had been taken, but suggested the scheme was unlikely to happen because no mechanism exists for direct grants.

In her speech on Thursday, the shadow chancellor also laid out Labour’s plan for economic recovery after Covid.

She said it was based on a “five-point plan” which included boosting British businesses, improving training and skills, supporting entrepreneurs, designing a new industrial strategy and investing in new technology.

Also on Thursday, Sir Tony Blair – the former prime minister and Labour leader – accused Boris Johnson of failing to provide new ideas to meet the challenges of modern politics.