Westminster's "watered-down" plan to give Holyrood limited power to create new benefits is not a credible response to the Smith Commission on devolution, Deputy First Minister John Swinney has said.

Mr Swinney welcomed many aspects of the UK Government's Draft Scotland Clauses on devolution - including "encouraging" progress on votes for 16 and 17-year-olds, air passenger duty, aggregates levy and income tax.

His early optimism took opposition parties aback at Holyrood today - suggesting he was taking a "good cop" approach following his earlier negativity.

But Mr Swinney soon switched to "bad cop", attacking some of the less "credible" aspects of the clauses and describing opposition claims of benefit as "baloney".

The SNP has pledged to take "improvements" to the Smith Commission to the electorate in May and Mr Swinney warned that there could be a public backlash at the polls if the next Scotland Bill fails to live up to their expectations.

His statement to parliament follows concerns that the UK Government could wield its power to have the final say on the date of implementation of new devolved benefits to hold up Scottish legislation indefinitely.

Mr Swinney said: "No-one in this chamber would want decisions of this Parliament in areas such as the bedroom tax frustrated by the need for consent from the UK Government.

"Even the Secretary of State for Scotland agreed over the weekend that there should be no right of veto. So, it is important that the UK Government revisits those clauses that require consent."

He added: "We're concerned to see that Lord Smith's recommendation for a power to create new benefits in devolved areas simply does not appear in the command paper and the Bill.

"The clauses would only allow this Parliament to create new benefits in the much narrower areas of welfare to be devolved under the Bill.

"Similarly the ability to top up reserved benefits has been watered down to cases of hardship. That is not a credible interpretation of Smith."

He continued: "Nor is it credible to argue that this parliament already has the competence to create benefits in devolved areas when social security schemes are specifically reserved under the Scotland Act.

"Many in this chamber will recall the difficulties this Parliament has faced in areas such as carers benefits and council tax reductions due to this reservation, and it is therefore vital that the power to create new benefits in devolved areas is put beyond doubt.

"These were rightly been hailed as some of the most important of the Smith proposals and this is perhaps the most serious omission in the Bill as it was published this week."

He added: "There should be a common objective of ensuring the Smith Commission agreement is implemented as swiftly and as effectively as possible.

"That means all of us recognising those parts of the proposals that represent good progress and working with the Scottish Government to argue for improvements in key, relevant areas. We in the Scottish Government are determined to argue for what is in the best interests of Scotland.

"But in the end it will be for the people of Scotland to judge, at the ballot box, whether these proposals meet their ambitions and whether they have been delivered."

Labour's pledge to translate the clauses into a "Home Rule (Scotland) Bill" provoked a backlash from Mr Swinney and other SNP members, who disputed whether the powers amounted to "home rule".

Labour constitution spokeswoman Jackie Baillie said: "Labour has said that we will deliver the Home Rule (Scotland) Bill in the first 100 days of a Labour government, with extensive new powers over tax, jobs and welfare that will form the basis of a modern home rule for Scotland at the same time as protecting the bonus of the Barnett formula.

"I note the Scottish Government's response to consultation with the UK Government about changes to universal credit.

"I genuinely don't believe that this amounts to the right of veto, it is about practical issues about timing.

"It was wrong, I think, to suggest that there was any other intent behind that."

Linda Fabiani, a member of the Smith Commission, was applauded by her SNP colleagues when she asked Mr Swinney whether the draft clauses "can in any measure whatsoever be described as home rule".

Mr Swinney said: "It's not a description I would apply to these provisions, there are some significant areas of responsibility which remain reserved to the UK Government which should be transferred to the Scottish Government to constitute the term home rule."

Conservative constitution spokeswoman Annabel Goldie said the initial tone of Mr Swinney's statement was a "welcome surprise".

"I liked the character of the statement, which was unexpectedly conciliatory and that is a striking contrast to some of the language that we have had from the Scottish Government following the Smith Report," she said.

"I even see some 'welcomes' and the word 'encouragingly', so I feel we're making progress, and things are indeed looking up and constructive partnership between the Scottish Government and the Westminster government, I think, is something that we can hope for with a great deal of confidence."

Liberal Democrat leader Willie Rennie said: "He's made a remarkable transformation from bad cop to good cop within the space of just one week and I hope that continues because the response to the Smith Agreement and the subsequent publication of the clauses was deeply negative from the Scottish Government.

"This is the transfer of £20 billion of new taxes and a £3 billion new welfare system."

Mr Swinney said: "Well, I can go back to bad cop quite quickly if Mr Rennie would like, and I am kind of tempted after the baloney we have just heard from Mr Rennie.

"Less than 30% of taxes will be set in Scotland and 14% of welfare spend will be devolved.

"I'm sure there were moments in the Smith Commission when Mr Rennie's colleagues would have like to have achieved more in relation to welfare devolution than was secured in the end."