Theresa May has defended Tory plans to protect winter fuel allowance for all Scottish pensioners while cutting it for many south of the border.
The Prime Minister said devolution meant different choices could be made in Scotland but insisted the plans for means-testing in England were fair.
Labour claims up to 10 million pensioners are set to lose the benefit under the Conservatives' plans.
Asked why it was fair for people in England to lose it when Scottish pensioners are protected, Mrs May replied: "Well, we have devolution in the United Kingdom and as a government we have given the Scottish government significant powers in relation to welfare and they make a number of decisions about various welfare benefits in Scotland.
"The decision we have made about winter fuel payments is that we will continue to ensure that the least well-off pensioners are supported but there is a principle of fairness.
"You see well-off pensioners getting help with their fuel bill and struggling ordinary families not having that help available."
Mrs May said the money released from the change in winter fuel would go into health and social care.
But quizzed on the plans as she visited a haulage firm in North Berwick, the Prime Minster side-stepped questions about whether 10 million pensioners would be hit.
"We are going to make changes for the payments of the winter fuel payments but we will continue to ensure that the least well-off pensioners are protected," she said.
The Conservative manifesto in Scotland says the winter fuel allowance will not be means tested.
It states: "We will also maintain all pensioner benefits in Scotland, including free bus passes and TV licences for the duration of this parliament.
"Social security devolution allows us to make different choices in Scotland and so we will protect universal Winter Fuel Payments for all older people and they will not be subject to means-testing.
"We will focus on ensuring that no pensioner has to live in a hard-to-heat home in Scotland by the end of the next decade through significant investment in energy efficiency."