The Labour leader claimed the public does not prefer “someone who dogmatically” maintains the same stances on crucial issues.
Sir Keir said “we are going to inherit a weakened, damaged economy” as he hinted he would not scrap tuition fees.
Defending his changing positions, Sir Keir said on BBC’s Sunday with Laura Kuenssberg: “When I was running for leader I made pledges which reflected my values. We’re now three years on, a lot has changed.
“We’ve been through Covid, we are still going through an awful conflict in Ukraine, and the Tory Government has done huge damage to our economy.
“We will not be able to do everything we need to do in the first five years of a Labour government.”
The Opposition leader has already U-turned on NHS outsourcing and abolishing Universal Credit.
Sir Keir said the NHS must reform or die. He said his party would never compromise on the principle that the health service must be free at point of use, ruling out a move to a European-style insurance model.
Reforms included allowing patients to bypass GPs and self-refer themselves to specialists. Sir Keir also suggested he would not scrap tuition fees, saying the economy had deteriorated.