Another week and there is more worrying news for Scottish Labour.

SNP figures show that a significant proportion of the colossal number of new members they have signed up since the referendum come from traditional Labour heartlands.

Labour knew already that Glasgow in particular and North Lanarkshire to a lesser extent were likely to be productive recruiting grounds for the SNP, having been among the few areas of the country to vote Yes, but they will not welcome the news that there appears to be quite such marked fervour for their opponents right on their doorstep.

The background of these new SNP sign-ups is not known, but the likelihood is that some will never before have felt moved to join any party (and may not even have voted, given the SNP's pre-referendum emphasis on unregistered voters). Labour's worry, though, will be over how many are disaffected Labour voters or even members.

There will have been little reassurance for them in the sight of 6000 people converging on Glasgow's George Square for a pro-independence rally yesterday. Organised by the socialist Hope Over Fear campaign and the controversial figure of Tommy Sheridan, the former Scottish Socialist convener, it demonstrated the strength of the continuing campaign for independence, and a desire to keep up pressure on politicians to deliver significant constitutional change for Scotland. This too is an uncomfortable issue for Labour, which has earned itself the dubious distinction of being the least radical of the five Scottish parties with its greater devolution proposals.

The challenge now is for the pro-UK parties, and Labour in particular, to respond. Johann Lamont has struggled to rally the troops and UK leader Ed Miliband, with his poor popularity ratings, has done no better. The party might face serious difficulties next May if it is seen to be acting as a brake on ambitious further devolution. Its current proposals may be designed to make it harder for English Tories to argue for the exclusion of Scottish MPs from voting on certain budgetary matters at Westminster, but timidity on this issue from Labour will not help the party in its Scottish heartlands.

Leaving aside the implications for Labour, the rally shows a welcome degree of ongoing public interest in the constitutional debate. It was always a concern after the last electrifying weeks of the campaign, that the astounding 85 per cent turnout would be the high watermark of political engagement by a large margin and the tide would sink fast afterwards. That does not seem to be the case, with the pro-independence campaign still highly vocal three weeks on. Being more visible does not mean the independence cause has necessarily gained ground, given that the Yes side was always much more visible than the No side, but still lost the referendum. What yesterday's rally does show is that with talks on greater devolution now under way, voters are still highly engaged and want far-reaching change. Politicians ignore that mood at their peril.