Today the invitingly named "Silk II" commission publishes its recommendations for extending the Welsh Assembly's powers.

Having already backed (in "Silk I") ­­Calman-style fiscal powers a year and a half ago, it's a useful reminder the constitutional debate doesn't cease at Berwick-upon-Tweed. In fact, there are similar conversations taking place in Northern Ireland, London and even constitutionally conservative England.

Thus former Welsh Secretary Ron Davies's aphorism about devolution being a "process, not an event" is apt, and applies across the United Kingdom. I have always thought the challenge for Unionist parties was twofold: devising credible devolutionary schemes in each of the UK's constituent parts while also fashioning a holistic narrative that finally bids farewell to ad hoc constitutional reform.

To date - and with the independence referendum less than seven months away - the former is better developed than the latter, which is both understandable and strategically unfortunate. For as long as this remains the case then the Scottish Government's charge that their Unionist opponents are not serious about devolving more power will resonate because it is to an extent true.

Of course, even if Labour, the LibDems and Conservatives published such a plan tomorrow it would be dismissed as inadequate, nothing more than a cynical rehash of Lord Home's "vote no for a better Bill" promise in 1979. Indeed, today Nicola Sturgeon will launch what one newspaper called a "scathing attack" on proposals she hasn't even seen. All three parties' proposals, she will argue during a speech in Glasgow, will "fall short of what Scotland needs".

A joint platform, however, looks unlikely. Yesterday Better Together's Blair McDougall admitted to the Sunday Herald that each party would most likely "reach decisions and positions which will probably be at variance with each other".

In truth, the differences are more likely to be tribal than the result of policy differences. Having already soiled their hands (to paraphrase Helen Liddell) by shoring up George Osborne's currency union veto, Labour figures are understandably reluctant to share yet another platform with the auld enemy.

Similarly, I understand the Scottish Conservatives are purposefully delaying their constitutional scheme until May so they can out-flank Labour and reposition themselves as the most radical party of devolution (much as their Tory counterparts have done in Wales). I suspect that aim might be quixotic, but that it is considered a serious goal says a lot about the situation the Scottish Labour Party finds itself in vis-à-vis devolution.

In short, it looks hostile towards extending the powers of an institution it established in the heady days of the first Blair government. Although the interim report of its Devolution Commission was genuinely radical, since its publication last April the party has given the appearance of being in panicked retreat. The usual suspects at Westminster, as well as their Holyrood ciphers, have set the tone, little of it positive. Appearing before them in London recently apparently Johann Lamont got a pretty rough ride.

In that context, a typically thoughtful speech from Shadow Foreign Secretary Douglas Alexander at Glasgow University last Friday night can be interpreted as a riposte to Messrs Davidson, Murphy and Macintosh, a polite reminder that they won't be setting the party's agenda in this respect. So his call for the Commission to "range widely and act boldly" when it reports next month provided a useful psychological boost, while briefing in yesterday's papers hinted at growing confidence among Scottish Labour reformers.

Complete devolution of income tax, including the power to vary each band in isolation (a point of tension among Welsh Tories) is a red-line issue, any retreat from which would constitute a red rag to the Nationalist bull. The expectation game is key: the interim report raised them, and therefore the challenge for Labour at its Perth conference later this month is to prevent damaging backsliding.

Thoughtful devolvers, meanwhile, don't believe the lack of a joint platform will necessarily undermine the credibility of their respective schemes. One strategist predicts that a "Unionist Venn diagram" will emerge shortly before the 16-week "short" campaign kicks off in late May. And there's quite a bit of overlap, common commitments likely to include income tax, employment law, social policy (probably supplementary benefits designed to keep the welfare union intact), elections and Crown Estate cash.

Liberal Democrat insiders are also keen to talk up partnership with Labour, perhaps with half an eye on the 2016 Holyrood election as well as a post-2014 constitutional settlement. They point to Gordon Brown's recent proposal for giving "permanence" to the Scottish Parliament (although such a move would inevitably require a written constitution), with which LibDems agree. Publication of "Campbell II", meanwhile, is "imminent", the aim being to set out a credible timescale for implementation.

"It's about developing space for a more-powers process to be outlined from March through to the referendum and beyond," one LibDem insider says. "And when all three Unionist parties have published it'll make sense for the common areas to be set out. Both the detail and its delivery have to look cast iron." So to an extent it'll be up to undecided voters to join the constitutional dots, albeit with a degree of guidance.

So if phase one of the Unionist strategy is publication of the Labour and Tory proposals between now and May, phase two will then emphasise common constitutional ground. There should also soon be movement on phase three, a commitment to a post-No "National Convention". This was set out most convincingly by Douglas Alexander in another speech last year and ostentatiously endorsed by the LibDems and Ruth Davidson.

The issue is how clear such a commitment will be before referendum day, but Better Together is aware of the "attractiveness" of having a few months to discuss exactly what form more powers would take while inviting input from trade unions and other elements of "Civic Scotland" (such as it is). Whether it creates space, as Alexander hopes, for "a new kind of politics", remains to be seen, but it would also have an obvious tactical purpose.

While the SNP frequently bangs on about the great betrayal of 1979, Unionists haven't made enough of the fact that at every juncture when Scotland's constitutional future was up for discussion 'Scotland's party' opted out of proceedings. If, following a "no" vote, the Scottish Government attempted to stand aloof from a similar discussion, then Unionists anticipate (and, let's be honest, hope) history will judge them harshly.

All of this fits into "carrot and stick" analysis of Unionist tactics since the beginning of this year, only so far it's been rather stick heavy. Ideally the constitutional carrots should have followed the currency sticks more swiftly, an "historic" announcement on bonds being little more than a damp squib. And although one large carrot is unlikely to be dangled come late May,

Unionists are hoping the sight of lots of smaller carrots will have the same effect.