A piecemeal approach to devolution that pits one part of the UK against another and allows the SNP to advance its agenda must come to an end, Liberal Democrat peer Jeremy Purvis has said.
Lord Purvis has proposed a constitutional convention to devise a stable power-sharing arrangement that safeguards the future of the UK.
His proposals would see the formation of a 12-month convention with a remit to consider devolution of legislative and fiscal competence to and within Scotland, England, Wales and Northern Ireland; devolution of legislative and fiscal competence to local authorities within the United Kingdom; reform of the electoral system and reform of the House of Lords.
The convention would include representatives from political parties and local authorities, but half of the membership would be drawn from outside politics.
Lord Purvis is seeking cross-party support for his Bill in the House of Lords and House of Commons. His proposals would not affect the progress of the Scotland Bill.
He said: "The new powers that will be delivered to Scotland through the new Scotland Bill are welcome. We also need to secure the full powers for Wales set out in the Silk Commission.
"But piecemeal devolution cannot deliver the stability we need.
"Pitting one part of the UK against another is no way to secure the future of our country.
"We need to abolish the make-do and mend approach to reform that has let the SNP move the devolution goalposts time and again in a way that might work for them, but not for Scotland or the rest of the UK.
"It is also long past time we grasped the nettle and reformed the electoral system and House of Lords.
"We need a Parliament fit for the 21st century rather than the 19th. That is what my Bill will help deliver.
"I hope all parties will recognise that we need a stable constitutional settlement and I will be seeking the support of Labour and the Conservatives in the House of Lords, and the SNP and others in the House of Commons.
"Crucially, my Bill will put people from outside of politics front and centre during this process.
"A constitutional convention will help us reach a settlement that protects the future of the UK and delivers communities the powers they need to thrive."
SNP MP Pete Wishart said: "As a Lib Dem peer in the unelected, undemocratic House of Lords, Jeremy Purvis has no democratic mandate.
"The time and effort of he and the few remaining democratically elected Lib Dem MPs would be better spent holding the Tories to account on their promise to the people of Scotland to deliver the Smith Commission proposals in full.
"After all, Jeremy Purvis's colleague Tavish Scott - a member of the Smith Commission - is part of a cross-party committee that just last month concluded the UK Government proposals fall far short of the Smith agreement.
"The Lib Dems were all but wiped out in Scotland at the general election after leaving a trail of broken promises behind them in government. Having betrayed voters on everything from tuition fees to welfare cuts and austerity, the people of Scotland don't trust them to deliver anything."