Kezia Dugdale, Gordon Brown and Kenny MacAskill are just some of the politicans to raise the idea of Scotland gaining extensive powers while remaining part of the UK under a new federalist structure.
“Federalism offers a potential route forward for unionists to improve the constitutional settlement and for nationalists to maintain the dream,” MacAskill, a former SNP minister, wrote in a newspaper column. “Those who invoked and advocate federalism have an obligation to step forward and seek to help define it,” he added.
The United States, Canada and Australia are among the countries with federal systems. Each has state or regional governments which legislate on everything from law enforcement to taxation. The federal government is then left to focus on specific national issues such as defence and foreign affairs.
But if such a system was ever to be adopted across the UK, several complex political issues would first need to be addressed.
THE WEST LOTHIAN QUESTION
The infamous West Lothian question is one major stumbling block to federalism in the UK.
It takes its name from former Labour MP Tam Dalyell, a consistent opponent of devolution, who believed tinkering with the UK’s unitary system would hasten Scottish independence.
He argued creating a Scottish parliament would lead to a constitutional impasse and effectively create two tiers of MP. “How can it be that I can vote on education in Accrington, Lancashire, but not in Armadale, West Lothian?” he asked in 1978.
The question has never been answered to any party’s satisfaction. David Cameron announced reforms in the aftermath of the 2014 independence referendum which would see Scottish MPs barred from voting on matters - such as the Housing and Planning Bill - which did not cover their constituencies.
When used for the first time in January, the SNP said the changes were “driving Scotland out of the door”.
A federal solution to the West Lothian question could be the creation of an ‘English Holyrood’ - an English assembly voting on domestic laws, leaving Westminster as a central UK-wide decision making body.
While there is public support for such an assembly it has yet to win backing from any senior figures. Advocating the creation of more political jobs at a time of economic hardship for many is unlikely to prove a vote winner.
A WRITTEN CONSTITUTION
The UK famously has no written constitution. The Westminster model of parliamentary democracy instead relies on statutes, court judgments and treaties. But whether this could function in a federal system is open to debate.
Some form of binding document, clearly dividing the differing roles of the new regional and central governments, would be required.
At present, Westminister devolves - or lends - certain powers to the Scottish Parliament and other assemblies. But it remains the ultimate legislative body of the UK and in theory could repeal Holyrood bills - even if such an action is extremely unlikely, given the potential political fallout.
Legal challenges between the different levels of existing federal systems are commonplace. The US Supreme Court regularly passes judgment on the compatibility of state and federal laws. A similarly robust system would surely be required in the UK.
James Madison, a political theorist who became the fourth president of the US, summed up the necessity of a written constitution to the American system. “The powers delegated by the proposed constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite.”
A WELSH LEGAL SYSTEM
The establishment of the Scottish Parliament was relatively straightforward given the country already had a separate legal system. But the Welsh system was effectively merged with the English in the mid-16th century. Unpicking the two in the devolved era has proved complex and time-consuming.
The Welsh Assembly only gained power to pass primary legislation under limited law-making powers in 2006, and won further autonomy following a 2011 referendum.
But the Senedd still lacks many of the powers devolved to Holyrood. An underpinning ideal of most federal structures is that states have equal rights - California has the same powers as North Dakota, for example.
If a federal structure was to be adopted in the UK, the Welsh Assembly would likely require significant upgrading to bring it in line with Scotland and Northern Ireland.
While this is a long-standing aim of Plaid Cymru, support for further political autonomy is generally weaker in Wales than north of the border.
A 2015 opinion poll by the BBC found 40 per cent support for granting the Senedd further powers, while 33 per cent said its existing powers were sufficient. A sizable minority - 13 per cent - called for the entire abolition of the Assembley.
While Welsh politics may be far from the minds of those in Scotland debating federalism, it is one of the many issues that would require attention.