The Scottish National Party has warned that taxpayers north of the border could be "short-changed" by Conservative plans to preserve the winter fuel payment for all Scottish pensioners while limiting it to the poorest in England and Wales.
SNP pensions spokesman Ian Blackford accused Theresa May of being "all over the place" on benefits for the elderly, as he highlighted SNP commitments on welfare and pensions ahead of next week's unveiling of the party's manifesto.
The SNP is joining Labour and the Liberal Democrats in committing to preserve the "triple lock" on state pensions, which guarantees they will rise by the highest of inflation, average earnings or 2.5%.
Mrs May has announced that a Tory government would drop the triple lock after 2020, with subsequent rises in line with inflation or earnings, whichever is the higher.
While the SNP manifesto pledge on the triple lock will extend only to 2022, Mr Blackford indicated that the party was likely to retain the commitment beyond the end of the next parliament, telling BBC Radio 4's Today programme: "We've had a commitment to the triple-lock as long as it's been here and I can't imagine any scenario where that would not be the case."
Mrs May sparked controversy on Friday by revealing that Scottish pensioners would all keep the winter fuel allowance of up to £300 a year under a Tory government, despite the introduction of means-testing in England and Wales.
Mr Blackford said it was not clear whether the Tories were backing the special treatment for Scottish pensioners with cash from UK government coffers.
"When you look at what they are doing with the winter fuel allowance, they are all over the place, saying different things to different people in different parts of the UK," he said.
"The question is where will the funding come from? Last year, that cost £158 million in Scotland. We need to make sure, if the Conservatives are saying that winter fuel payments are going to be protected, that the funding for that comes from the Westminster Government in order that we can do that.
"This will become a devolved competency over the course of the lifetime of this parliament so we need to make sure that people in Scotland are not going to be short-changed by the Conservatives."
Mr Blackford said the SNP would like to see the allowance extended to severely disabled children.
And he said the party will continue to fight for so-called "WASPI women" born in the 1950s who will lose out from the planned equalisation of the state pension age. But he said the Scottish Government had neither the powers nor the resources to implement by itself the SNP's proposals for an extended transition period.
Defending the SNP decision to keep the triple lock in the face of evidence it will lead to a growing tranche of state spending going to the elderly, Mr Blackford said: "We have a commitment to keep the triple lock through the lifetime of the next parliament.
"We still have far too many pensioners in poverty in this country. It's about making sure that we protect the interests of the vulnerable in our society.
"We've got a situation in the Highlands of Scotland where 77% of pensioners are in fuel poverty. Until we've dealt with that situation, it's quite right that we should protect the interests of this most vulnerable group.
"What we're not going to do is play off one generation against the other, and that's exactly what this Government is doing."