Mr Rennie said it took three to four years to put the Scotland Act 2012 into law, with its land and buildings transaction tax due to begin this April and limited income tax powers expected in 2016.
But he said the full income tax powers promised in the Smith Commission - currently being piloted by Lib Dem Scottish Secretary Alistair Carmichael - could be delivered quicker because of the groundwork laid in 2012.
The Fife MSP also defended his party’s record in the British Government, insisting the UK Lib Dems could not deliver on their pledge to eliminate the deficit because “circumstances have changed” since they came to power in 2010.
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Looking ahead to the forthcoming general election, he said Lib Dem minister Jo Swinson has “a fantastic record in East Dunbartonshire” and will be returned “in big numbers”, and tipped his “fantastic candidate” Christine Jardine to beat Alex Salmond in Gordon.
Regarding the Smith Commission, Mr Rennie told BBC Radio Scotland’s Good Morning Scotland programme: “We will implement it in an orderly fashion, and that means having the legislation drafted by the end of January and making sure in the next parliament we get it implemented and implemented in an orderly fashion so that the Scottish Parliament can have these powers within time.
“We will implement these powers quickly because we know there is a demand in Scotland for more powers.
“If you look at the 2012 Act, we debated it for three or four years before the legislation was implemented in 2012 by (former Scottish Secretary) Michael Moore, we have the land and buildings transaction tax which is being implemented this coming year, then in future years we will have the income tax variability powers.
“That has taken three to four years so you can see the amount of time, but I think it will be quicker on income tax because we have already set the path on income tax powers in the 2012 Act.
“These things will have to be developed over time, so there is a desire among all the parties to get this done and get this done quickly.”
He added: “We’ve got the economy back on track, based on a plan that the SNP and Labour said wouldn’t work.
“We’ve made significant progress against strong headwinds. If you look at the economy in Europe, there have been significant issues that have had a consequential effect on the Scottish economy and the UK economy.”
Mr Rennie said it is taking longer to get the economy back on track than originally promised in 2010.
“Of course it’s taken a longer time, but the circumstances have changed,” he said.
“You can’t just expect these things not to have an effect on the British economy. Of course they’re going to have an effect on the rest of the world. We’re not isolated. We cannot simply stand alone as an island.
“Other economies have an effect on the British economy and we have responded, and responded very well.”
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