Wales' First Minister Carwyn Jones is to urge fellow leaders in the UK to sit down and discuss the nation's constitution before it is too late.
Mr Jones will set out his vision of a "new" United Kingdom when he addresses an audience in Westminster.
In his first major speech on the issue outside of Wales, the Welsh Labour leader will ask how the different territories of the UK should be governed, and how their governments and legislatures should relate to each other within the UK.
And he will also reject independence for Wales by setting out his vision of a United Kingdom which is politically diverse - but insists the relationship between the devolved nations and the UK Government needs to be reset.
Mr Jones will say: "Devolution is now the settled will of the Welsh people.
"In common with the vast majority of the people of Wales, I have no interest in independence for Wales.
"While Scotland's constitutional future is a matter for the people of Scotland, Wales would enormously regret any decision by the Scots to opt for independence.
"Those of us who are committed to the UK cannot pretend that, if Scotland goes, the remaining truncated Union could simply carry on as before.
"So, rather than simply allow events in Scotland to unfold, and to react passively to whatever happens when it happens, I believe political and civil society across the UK should be talking now about what kind of UK we want to see."
Mr Jones added if Scotland decided to remain part of the UK it was very likely there would be more powers for the Scottish parliament.