The potential of the Scottish Parliament has not been fulfilled as it has become dominated by a "narrow constitutional agenda", David Mundell has claimed.
The Secretary of State for Scotland added that MSPs were failing to distinguish between their twin roles as parliamentarians and party politicians, with Holyrood's much-vaunted committee system too often letting ministers off the hook.
But the SNP said Scotland “should complete the journey started by the devolution process”.
Mr Mundell called for the creation of elected committee conveners, similar to the Westminster system, in an essay for the Reform Scotland think-tank, which is running a series of articles on the 20th anniversary of the Scottish Parliament.
"Its huge potential has not yet been fulfilled," he wrote. "That’s not the fault of Holyrood as an institution. Rather, it is down to the Scottish governments that have held the levers of devolved power.
"Successive administrations have failed to live up to the founding idea of a Parliament with the tools and imagination to develop distinctive Scottish policy solutions to Scottish problems within the UK.
"Instead, for more than a decade, our Parliament and politics have been dominated by a narrow constitutional agenda that the majority of Scots have never supported."
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Mr Mundell was among the original 129 MSPs voted in at the 1999 parliamentary elections, being returned on the south of Scotland list. He resigned from Holyrood in 2005 after winning a Westminster seat at that year's general election.
He continued: "In the early days, we convinced ourselves that Holyrood’s committee system was a ‘jewel in the crown’ – a reservoir of independent thinking and a robust challenge to government.
"There was some justification for that at the time. By and large, the newly created parliament was populated by a more independently-minded cadre of MSPs than now. I’m thinking about people like Donald Gorrie, John McAllion and Margo MacDonald. And, at the time, Westminster’s committee system lacked the teeth it bares today.
"Sadly, things have changed for the worse. Newer intakes of MSP seem less clear about their duty to distinguish between their twin roles as parliamentarian and party politician.
"Stories of ultra-loyal backbenchers turning up to question a Scottish Government minister armed with a list of questions drafted by the minister’s SpAd (special advisor) are all too common and a shocking indictment of the system."
SNP MSP Tom Arthur said: “David Mundell, as ever, is plucking nonsense from the ether and presenting it as fact. His claims are rich considering the fawning acolytes in the Scottish Tory ranks who are set to blindly follow their Brexiteer masters off the cliff edge.
“The Tories have always hated devolution and fought tooth and nail against establishing the Scottish Parliament in the first place,
“However, in 20 years of devolution, great progress has been made on a number of issues. Our ability to take decisions to improve the lives of people in Scotland, in a parliament which is accessible and ready to listen, has undoubtedly made our country a better place.
“While we’ve taken better decisions in devolved areas, it’s become increasingly clear through through the Brexit process that the Westminster system has failed Scotland - putting paid to any notion that we are an equal partner in the UK.
“We should complete the journey started by the devolution process - allowing Scotland to make all decisions for ourselves with the full powers of independence.”