David Cameron has claimed the SNP's call for full fiscal autonomy had become "FFS - full fiscal shambles'.
The prime minister was responding to the SNP's Westminster leader, Angus Robertson, who said the Scotland Bill had not delivered on the Smith Commission agreement.
Mr Cameron challenged the SNP to spell out how it actually planned to use Holyrood's new devolved powers.
And he accused them of "only wanting to talk about process" rather than policy.
The Scotland Bill will give Holyrood control over income tax rates and bands, a half share in VAT revenues and a greater say over some welfare benefits.
'Made a vow'
Speaking during Prime Minister's Questions, Mr Robertson told MPs: "The prime minister and other UK party leaders made a promise, they made a vow that more powers will be delivered to the Scottish Parliament.
"The people were promised home rule, they were promised and I quote 'as close to federalism as possible'. Why does your Scotland Bill not even deliver the limited Smith Commission proposals?"
Mr Cameron insisted the bill did fulfil the vow, but added: "Of course what it doesn't fulfil is the full fiscal autonomy that your party would like that would land Scottish taxpayers with a bill of thousands and thousands of pounds.
"If that's your policy, when you get up, you should say so."
Mr Robertson continued: "The House of Commons library says that important parts of the Smith Commission proposals are not in the Scotland Bill that you have proposed.
"The shortcomings in the bill have been identified by an all party committee in the Scottish Parliament on which the Scottish Conservative party sits. Are all of these people wrong?
"Will you now commit to deliver the Smith Commission proposals in full and all of the powers that were voted for by the people of Scotland in the general election?"
Mr Cameron hit back: "This goes to a larger truth, which is the SNP only want to talk about process. They don't actually dare talk about which power they are being given they would like to use.
"You don't like the way things are fixed, why don't you put up taxes and spend more money? Isn't it time you started talking about the policies you want to put in place, the outcomes?
"Because the truth is this - full fiscal autonomy has now become FFS - full fiscal shambles."