David Cameron said the Scots and UK parliaments had to respect each other.
Tory leader David Cameron has said the Scottish Parliament must respect decisions made on a UK basis, if he wins the next election.
Mr Cameron told BBC Scotland that, if he became prime minister, he would recognise the work of MSPs on devolved issues.
But he said decisions on policies such as Trident renewal, opposed by the SNP, had to be respected by Holyrood.
Mr Cameron also said the Barnett funding formula needed replacing.
But he said he had no immediate proposals for an alternative to the mechanism, used to distribute Treasury cash to the different parts of the United Kingdom.
The Conservative leader told BBC Scotland's Politics Show his party would not have enough MPs in Scotland to claim an "automatic mandate" if it won the next UK election.
Relations with the Scottish Government, Mr Cameron said, would be taken forward on the basis of "co-operation".
"It means respecting that what is decided in Scotland by the Scottish Parliament should be respected by the Westminster parliament," he said.
Mr Cameron re-stated his support for maintaining a British nuclear deterrent - an issue reserved to Westminster - by saying he would not scrap the Clyde-based Trident nuclear submarine fleet.
He went on: "Just as I will respect the Scottish Parliament's decision over issues like student fees or prescription charges, I expect them to respect the mandate of the United Kingdom government on those things that the United Kingdom is responsible for."
A spokesman for Scottish First Minister Alex Salmond said the SNP Government would co-operate with any UK administration in the best interests of Scotland.
But the spokesman added: "David Cameron's problem is that no amount of warm words will wipe out memories of the Tories imposing policies like the Poll Tax when they had no mandate in Scotland - or opposition to their planned future spending cuts."
The population-based Barnett formula, now more than 30 years old, is regarded by politicians in some parts of England as grossly unfair.
Critics say it gives Scotland more cash than it should be entitled to at the expense of English regions.
Mr Cameron argued that an alternative would not make a big difference to the Exchequer.
"If you replace the Barnett formula, you'd replace it with a needs-based formula - and Scotland has a lot of needs and has some very deep pockets of poverty."