Rachel Reeves is facing a growing backlash over fears she could launch a tax raid on pensions in a bid to plug a multi-billion-pound black hole in the nation’s finances.

The Chancellor is under mounting pressure to rule out slashing pension perks after warnings that another round of speculation could trigger panic withdrawals and undermine confidence in long-term saving.

Former pensions ministers Sir Steve Webb and Baroness Ros Altmann have joined leading financial experts in demanding that Ms Reeves commit to leaving pension tax relief alone.

The Treasury has refused to rule out changes – fuelling fears that millions of workers could see their retirement pots targeted in the autumn Budget as weak economic growth leaves a hole in government revenues.

Sir Steve, now a partner at consultants LCP, said: “Once again we have the return of uncertainty about the pensions tax regime. This annual spectacle is deeply unsettling for what is supposed to be a long-term business.

“It would be hugely valuable for the Chancellor to set out her position on pension tax breaks and then leave things unchanged for the rest of this Parliament so that people know where they stand and can plan accordingly.”

His warning follows calls from investment firm AJ Bell for a ‘pensions tax lock’ to guarantee that no changes will be made for the rest of this Parliament.

Baroness Altmann echoed the concern, telling This is Money: “Speculation about tax changes is undermining people’s ability to plan ahead and damaging confidence in pensions.”

The Chancellor is reportedly eyeing a number of controversial options, including cutting the amount savers can withdraw tax-free from their pension pots – currently capped at £268,275.

A similar rumour emerged ahead of last October’s Budget, prompting some savers to cash in early to avoid a potential tax grab – a move that experts warned could leave them worse off in retirement.

Other possibilities include slashing tax relief on pension contributions, cutting the annual allowance or even reinstating a lifetime cap on total pension savings – despite Labour previously opposing such a move when it was scrapped by the Tories.

Sarah Coles, of investment giant Hargreaves Lansdown, warned of the dangers of a second year of uncertainty, saying: “It’s important to learn the lessons from the speculation ahead of last year’s Budget. We can’t have a repeat of this for a second year.”

The Chief Secretary to the Treasury, Darren Jones, says no changes to tax and spending plans will be made until the Office of Budget Responsibility has produced its verdict on government finances.