Rishi Sunak declined to rule out real-terms cuts to benefits amid suggestions the move could be taken to free up cash for tax cuts ahead of the next general election.
Chancellor Jeremy Hunt is reportedly weighing up breaking with custom by not raising welfare payments in line with inflation in his autumn financial statement.
The move would provoke allegations that the Government is targeting some of the most vulnerable during a cost-of-living crisis in order to cut taxes.
And it would be particularly contentious if ministers also maintained the “triple lock” on pensions by raising those payments in line with rising prices or earnings.
Mr Sunak declined to “speculate” about what will be in the Chancellor’s statement on November 22 when asked if he could guarantee benefits will rise with inflation.
“And those decisions are announced at the autumn statement, that’s entirely normal,” he said.
As the Prime Minister sought to “reassure” those struggling with the cost of living, he pointed to the extra support already put in place to help with energy payments and other bills.
“So people should be reassured that that extra support is there for the most vulnerable in our society at a time which I know is difficult and that’s why we have to bring inflation down,” he said.
“That’s why my first in my five priorities is to halve inflation. That is the best way to help everyone with the cost of living.”
Benefits are usually raised in line with September’s consumer price index measure for inflation.
But reports suggested that Mr Hunt could point towards forecasts that inflation will be far lower in April, when the payments hike would come into effect.