Prime minister David Cameron should set up talks on the United Kingdom's constitution before it is too late, Wales' first minister Carwyn Jones has said.
The Welsh Labour leader, who decided against renewing a coalition with nationalists Plaid Cymru following last year's election, has often spoken of his desire for the four home nations to remain part of the UK.
Following the Edinburgh agreement, Mr Jones admitted he would be gutted if Scotland gained independence in a referendum next year.
But the former barrister feels the Tory-led administration in Westminster should set up a special constitutional convention ahead of Scottish voters going to the polls.
He said: "I would like to see Scotland remain part of the UK. I firmly believe we are stronger together than we would ever be apart.
"I would regret enormously any decision by the Scots to opt for independence.
"A major change in Scotland's relationship with the rest of Britain - or its separation from the rest of the UK - would require a radical reconsideration of Wales' constitutional relationship within a re-defined United Kingdom.
"That's why, I have called for the establishment of a Constitutional Convention to agree a new constitutional settlement for the UK which is fit for the 21st century."
Mr Jones said for the UK to survive in its current form it would need to be politically diverse, looser, and combine several centres of democratic accountability.
He said: "So, rather than simply allow events in Scotland to unfold, and to react passively to whatever happens when it happens, I believe that political and civil society across the UK should be talking now about what kind of UK we want to see.
"Whatever happens in 2014, the constitutional status quo is unsustainable."
However, his rivals in the Welsh Assembly and former government partners Plaid welcomed the Edinburgh Agreement.
Leader Leanne Wood said: "The signing of the Edinburgh Agreement is a historic moment in which the people of Scotland were given the power to decide on their own futures.
"In recent years, more people in Wales and Scotland have wanted to take control of their own lives through the Scottish Parliament and National Assembly for Wales. Scotland will move ahead whatever happens in 2014 and it is up to us to make sure that Wales does too.
"Plaid Cymru is determined to secure fair funding, control over job-creating levers and the power to make a difference for our people as a minimum for the short term."