Yet, in the short-run at least, the SNP is a long way from becoming the largest party north of the border and so furthering its goal of independence for Scotland. Monklands East was remarkable not for the swing to the SNP but for Labour's survival in the face of local scandals. Labour's support remains stubbornly strong: in the 1992 general election no SNP candidate came within 10 percentage points of the Labour victor. Tony Blair's succession means his party remains attractive, since it seems more likely to win power and so fulfil pledges to create a Scottish parliament.
For now the SNP would be foolish to concern itself with making electoral breakthroughs beyond taking Tory marginals such as Perth and Kinross, and Tayside North. The party should instead rethink its policies for the day when independence may be high on the political agenda - that is, once a Scottish parliament is established.
SNP efforts to outflank Labour from the left and exaggerate the benefits of independence have left it with an outdated, statist image. Its vision of a Scotland with a large public sector, funded by North Sea oil, needs rethinking. This prospect, reminiscent of old-style Scandinavian social democracy, is not affordable and damages the party's credibility.
There are signs that the SNP is beginning to face reality. Alex Salmond, the party leader, has ordered a rewriting of economic and budgetary policy. The SNP has also become more friendly towards Europe. Its view is that an independent Scotland should be a member of the European Union, implying that the country would neither be cut off from the international economy nor protected from the disciplines of free markets.
All of this takes place at a time when the political debate inside Scotland has moved well beyond the earshot of those who live south of the border. The suspicion is that Mr Salmond is content to see Labour win a Westminster election and to establish a Scottish Parliament. The SNP openly speculates about how it could then use the likely instability of this fledgling body to precipitate Scotland towards independence.
The fear must be that the SNP would attempt to sabotage a Scottish parliament by fomenting conflict with Westminster. This is what Slovak nationalists did to destroy Czechoslovakia and so create an independent but impoverished Slovak republic. Labour's second Scottish leader in succession will need to bear in mind the importance of providing the new parliament with sufficient powers, clearly defined. That is, if Labour continues to believe in the Union.