Sir Keir Starmer cannot “credibly offer change” unless he backs the SNP’s calls for a cost-of-living support package, Stephen Flynn has said.

The SNP Westminster leader wrote to the Labour boss to urge him to drop his party’s “limp loyalty to Tory austerity”.

Chancellor Jeremy Hunt will present the UK Government’s autumn statement – an update on economic plans – on November 22.

Mr Flynn’s letter has urged Sir Keir to back calls for a £400 energy bill rebate for households over the autumn and winter, mortgage interest relief and maintaining the triple lock on pensions.

It’s time to free yourself from the self-imposed straitjacket of Tory spending plans

He has also been told to scrap the two-child benefit cap, which Labour has previously ruled out committing to, calling it “uncosted”.

Ahead of next year’s election, the SNP Westminster leader told Sir Keir he must offer a “substantial programme of governmental intervention and investment to clean up this Tory-made mess” if he is to offer a “credible” alternative.

Mr Flynn said: “With daily detail being exposed of the damage caused by this Tory government’s legacy, now is finally the time to ditch your timid, cautious and conservative approach.”

Addressing previous comments from the Labour leader that he was content being described as a “fiscal conservative”, Mr Flynn said the approach will not “fix crumbling public services and copying Tory cuts won’t help people through this Westminster cost-of-living crisis.

“It’s time for Labour to ditch its limp loyalty to Tory austerity.”

He added: “It’s time to free yourself from the self-imposed straitjacket of Tory spending plans.

“The public are increasingly wise to the fact that unless you are prepared to ditch Tory austerity, you can’t credibly offer change.”

Labour’s promises for the general election so far include “costed” policies such as closing loopholes in the windfall tax and ending tax breaks for private equity bosses to provide additional funds for the NHS and free breakfast clubs for primary children in England.

They do not include lifting the two-child benefit cap – where families in receipt of universal credit do not get additional funds for the third child or subsequent child born after April 2017.

It also includes a new deal for workers which would place a ban on zero-hour contracts and protects against unfair dismissals.

Labour has been approached for comment.