THE issue of what might happen in the event of a No vote in September's referendum has become a little bit clearer after the latest interventions in the debate from Gordon Brown and Sir Menzies Campbell.

Labour, it seems, are finally edging towards a position on tax devolution that the party's warring MPs, MSPs, devo-fans and devo-sceptics alike can agree upon.

The LibDems, meanwhile, appear to be facing a tougher time than they hoped for when it comes to persuading their fellow pro-UK parties to sign up to a broad programme of constitutional reform.

That's how it looks after former PM Mr Brown submitted detailed plans to Labour's devolution commission and former LibDem leader Sir Menzies published the follow-up to his party's home rule commission report.

Looking first at Labour, Mr Brown says Holyrood should set a bigger share of income tax than it will do from 2016 under the Scotland Act. In addition, he suggests the parliament should have full control over the "additional" or top rate.

That's a compromise for a party which has been badly split between those who want full devolution of income tax and those who believe the Scotland Act has gone quite far enough, thanks very much. What's more, it looks like a compromise that is winning out after months of behind-the-scenes wrangling. Scots party leader Johann Lamont was not just sitting alongside Mr Brown yesterday, in a very visible show of support, she even used her shot at First Minister's Questions last week to tee up his top rate idea, establishing during her weekly joust with Alex Salmond that the First Minister has no plan to raise the top rate from 45p to 50p (as it was under Labour) in an independent Scotland.

Overall, Mr Brown's proposal is a lot less radical than the devolution commission's recommendation last year to hand Holyrood control of income tax "in full" and the party can expect to be accused of a climbdown. However, his call for the top rate to be devolved at least allows Labour to claim they are enabling MSPs to make the system fairer and, strategists reckon, it might just embarrass Mr Salmond into the bargain.

As Ms Lamont indicated last week, before he can light his "progressive beacon" the First Minister will have to explain why the top rate of tax should be 45p in an independent Scotland but 50p across a Labour-led UK. Giving Holyrood the right to set a higher rate than the rest of the UK will put him on the spot, Labour hope.

As for the LibDems, they appear some way off their ambition of rallying the pro-UK parties behind a broad agreement on more powers. Sir Menzies made a bold plea yesterday for the parties to agree the general principles ("heads of agreement," he called them) that would underpin further devolution. A more detailed prospectus would then be thrashed out at a summit within 30 days of a No vote, under his plan. Labour were privately dismissive of the idea yesterday and are keen to focus on their own offer. It remains to be seen whether the failure of the pro-UK parties to work together will make voters question just how serious they are about delivering more powers for Holyrood.