DURING my time as an MSP, I always had a lot of time for Malcolm Chisholm. Despite our differences on independence – and a lot more besides – I respected him as the most principled minister in the ruling Labour-LibDem coalition at Holyrood. Indeed, as far back as December 1997 he had resigned his post as a minister in the Scottish Government over cuts to single-parent benefits driven by Gordon Brown and Tony Blair.

So, I wasn’t surprised when he broke ranks with his Labour colleagues in Wales to stand firm against the Westminster Brexit power grab. Last week he urged Labour and the LibDems to “stand with Nicola Sturgeon in defence of the 1998 Scotland Act”.

And the response from the two relevant party leaders? Silence. Strange, because both men claim to be passionate defenders of devolution.

Last autumn, Willie Rennie marked the 20th anniversary of the 1997 devolution referendum by declaring his burning pride that “Liberal Democrats were part of the civic movement in Scotland, through the Constitutional Convention, that set down the clear path for a devolved parliament with real powers”. Not to be outdone, Richard Leonard boasted of the five years he spent working with the STUC in the 1990s when it was campaigning for a strong Scottish Parliament.

Now comes the first serious attack on devolution and the pair are rushing to the barricades with the urgency and passion of stone statues. Whether that’s down to their tribal hatred of the SNP or whether it’s because they dare not defy their superiors in London I don’t know.

For a lot of people going about their daily lives, the interminable, complex debate around the repatriation of powers to the devolved administrations must seem like political geekery gone mad, as impenetrable as a group of computer programmers arguing over the relative merits of Javascript or Python.

But Willie Rennie and Richard Leonard have both been involved in frontline politics for long enough to know that this matters. Any rolling back of devolution, even if it’s framed as a temporary arrangement, will set a precedent. We might have a weak Westminster Government right now, led by a Prime Minister swimming out of her depth, but a few years down line we could yet see a majority hard-right government led by the likes of Jacob Rees-Mogg and Boris Johnson.

Standing in the dark shadows of the Conservative Party, waiting for Theresa May to stumble and fall, are men in the mould of Spanish Prime Minister Mariano Rajoy. The Tory party fought devolution to the bitter end, and there are many influential figures in the party hierarchy who would close down Holyrood in the blink of an eye if they thought it might get in the way of their UK nationalist project to Make Britain Great.

Richard Leonard and Willie Rennie also a have a bit of explaining to do about how they can reconcile their claimed support for a federal UK with their acquiescence to the Westminster power grab. A week ago, Richard Leonard called for the British Labour Party to “get a move on” towards federalism.

He was backed by Willie Rennie, who said “support for federalism has been part of the DNA of the Scottish Liberal Democrats for a very long time”. His comments were even welcomed by Murdo Fraser, another self-proclaimed federalist who supports the erosion of the existing devolution settlement.

Fellow National columnist Gordon MacIntyre-Kemp may have been exaggerating ever so slightly when he suggested there are a thousand definitions of federalism, but his point was serious. The word is now used so loosely that no-one is quite sure what it means in practice. In recent years it has been used by Gordon Brown as a synonym for enhanced devolution. Others have suggested that setting up regional assemblies in England would turn the UK into a federal state.

But the difference between genuine federalism and devolution is not one of degree. The essence of devolution is that power is handed down from above, while the essence of federalism is that power is ceded upwards.

The word was originally coined to refer to the compromise United States constitution, created after the 13 colonies had come together to free themselves from British rule. It was a voluntary power-sharing arrangement among sovereign states, and it involved compromises and mutual consent. The smaller former colonies, fearing their voices would be drowned out by sheer numbers, initially demanded full equality with equal representation from each state, while the larger units insisted on representation based on population size. The compromise involved the establishment of two houses: the Senate, in which each state is equally represented; and Congress, which is weighted to reflect the size of the population in each state.

Crucially, the federal principle involved shared sovereignty, with each state having its own constitution. Today the California state constitution is one of the longest in the world and enshrines, for example, equal rights for women and opposition to capital punishment. Its state governing bodies are subordinate not to Washington but to the Californian Constitution, which among other stipulations sets a maximum eight-year limit for those holding office.

After the 2014 referendum, some commentators – including David Torrance, who recently departed from The Herald – insisted that the UK was now on course to become a federal state. But that was never going to happen. As the Brexit power grab underlines, the supremacy of Westminster is the bedrock of the British state.

The irony of federalism is that it’s presented as an alternative to independence, yet it can never be achieved within the Union. Only if the United Kingdom were dissolved and its constituent parts achieved full sovereignty would it be possible to even start negotiating an equal, genuinely federal relationship across the isles of Britain and Ireland.