David Cameron, Nick Clegg and Ed Miliband have jointly promised to give the Scottish Parliament enhanced powers if voters reject independence in September's referendum.
The Conservative, Lib Dem and Labour leaders have signed a joint declaration saying they all support "the further strengthening of the Parliament's powers".
They say future measures will look particularly at "areas of fiscal responsibility and social security", suggesting Scotland would get more powers over raising tax and distributing benefits.
But the Scottish National Party dismissed the move, alling it a "rehash of vague promises".
A spokeswoman for First Minister Alex Salmond said: "The reality is that only a Yes vote on September 18 will give Scotland the powers we need to create a more prosperous and fairer society."
The first debate between Alistair Darling and Alex Salmond had barely finished when their respective teams went into battle.
Campaign rivals Alex Salmond and Alistair Darling both traded blows in a surprisingly feisty televised debate on Scottish independence.
Alistair Darling is getting 'feisty' during the STV Debate.