There has been a "significant watering down" of the proposals for further devolution for Scotland, the First Minister has said, as the basis of a new law that will give more powers to Holyrood was published.

Nicola Sturgeon said draft clauses that will underpin the legislation must be strengthened, as she accused the Westminster parties of failing to deliver on their pre-referendum vow.

During a clash at First Minister's Questions, Scottish Liberal Democrat leader Willie Rennie insisted the vow to transfer powers to the Scottish Parliament had been delivered, adding that Ms Sturgeon had "gone on the hunt for reasons to be miserable".

The Scottish Government says the draft clauses water down some of the key Smith Commission proposals on welfare, employment support and borrowing.

The welfare provisions will not allow the Scottish Parliament to create new benefit entitlements in devolved areas, the Government said, and would also mean UK ministers would need to give their approval to any changes to the Universal Credit, including the so-called ''bedroom tax''.

Scottish Secretary Alistair Carmichael has said the First Minister ''is wrong'' to suggest UK ministers retain a veto in key areas.

Ms Sturgeon said: "Of course it is no secret that I didn't think the Smith Commission proposals went far enough, but nevertheless I do welcome the proposals as far as they go, and I think it is really important now that both the spirit and the letter of those proposals are translated into legislation.

"I welcome the draft clauses today in as far as they go, but I think in some key respects, there has been a significant watering down of what the Smith Commission proposed.

"I cannot believe that Willie Rennie is going to stand up here and argue that in any circumstances it can be right for Westminster to retain a veto on whether or not this Parliament can abolish the bedroom tax, and I also don't believe Willie Rennie will agree with the fact that even although the Smith Commission said we should have a general power to create new benefits in any devolved area, that's not actually being delivered.

"So Willie Rennie should stop swallowing the Tory line on this and instead get behind the Scottish Government and try and strengthen the proposals."

Mr Rennie said: "The vow has been met, delivered on time, this is home rule."

He added: "In Smith she (Ms Sturgeon) agreed to share the Universal Credit with the UK Government, now she wants to exclude the people she agreed to share with.

"Doesn't she realise how ridiculous she sounds? All we have to agree is a start date for the new Scottish system - that's not a veto, it's government working together in common sense."

He continued: "Can I ask her when she will honour her part of the Smith agreement and extend devolution to local communities?

"Two months since Smith and there has been no action whatsoever."

Ms Sturgeon responded: "I am very committed to devolving power away from this Parliament.

"I don't think it is reasonable for Willie Rennie to say we should be devolving away powers proposed by the Smith Commission before the UK Parliament has even got round to giving this Parliament the powers in the first place."

She also attacked Labour and the Conservatives, adding: "Isn't it rather strange that on the day that the UK Government is publishing its draft legislative clauses supposedly implementing the Smith proposals we don't have Labour or the Tories with the gumption to stand up here and say that the vow is being delivered, because they know it is not."