The dilemma for the SNP will lie in acting as 'the real opposition' while avoiding becoming part of the Westminster furniture

Certain parties are also prone to bouts of weakness. Another reason for Cameron to throw himself into a 100-day programme is the state of Labour, still Her Majesty's Official Opposition, but in no condition to oppose anything much. It will spend the summer struggling to find plausible successors to the demonstrably implausible Ed Miliband and Jim Murphy while the Tories forge ahead.

Which leaves the Scottish National Party. Even with 56 of Scotland's 59 MPs, its claim to be the "real" opposition is not, in an obvious sense, worth consideration. Cameron has 331 seats of the 650 theoretically available: oppose that. A historic SNP result on this side of the Border might have moral force, constitutional implications, and a very precise legitimacy. For now, it has no bearing on the Westminster arithmetic.

But then, who else is there to oppose a Tory government giddy with triumphalism? Labour means to spend at least 100 days talking to itself. The Liberal Democrats are reduced to the kind of numbers that give rumps a bad name. The SNP group sought election promising to "speak for Scotland". Given Cameron's stated intentions, it could find itself obliged to do more than that. This will be tricky.

We have seen as much already in an anguished debate over fox-hunting. Cameron, as keen on the disgusting vice as any, promised a vote on the matter in his manifesto. He also claims that this time around, with no LibDems in his way, he will fulfil all such pledges. Some of his MPs mean to keep him at his word and see their ancient right to trample landscapes and have small animals ripped to pieces restored.

Any retreat into the jolly barbarism of Jorrocks will not affect Scotland. The SNP meanwhile plays no part in "England-only" votes. The policy has been amended by Nicola Sturgeon to take account of English decisions that could have a material effect on Scots, but hunting hardly fits the bill. After years of complaining about politicians in England imposing their will on Scotland, how could Nationalists now intervene?

Some Labour sorts, apparently with nothing better to do, think they see a trap for the SNP in that. The sound of Miliband spurning any prospect of aid from Sturgeon is forgotten. A party with one Scottish MP has dismissed old anxieties over the West Lothian question. By some weird feat of auto-suggestion it has even managed to make more of a fuss over fox hunting than Tory threats to the Human Rights Act. The idea is to impale the SNP on the point of a moral question.

This is, in the absence of actual legislation, fair enough. How do you take a place in a shared parliament and say that an ethical issue is none of your business? Let's say abortion law is sooner or later devolved to the Scottish Parliament. Let's say a Tory government follows its Republican cousins in the US and attempts to restrict termination services in England. How would the SNP's policy cope with that situation? It is not a likely scenario, but it is not impossible.

Nationalist MPs should not fret too much. There are 56 of them now, not six. That changes everything. Henceforth, speaking for Scotland while sitting in a UK parliament will require more than the wit, cheek and hard work of a pressure group. The threat of "English votes for English laws" is empty, meanwhile, if you happen to be a party that wants an end to Westminster. Respecting England's right to self-determination, while honourable, is not the highest priority.

Fox hunting will not be the last of it, in any case. The dilemma for the SNP will lie in acting as "the real opposition" while avoiding becoming part of the Westminster furniture. When Labour recovers a little composure and finds another leader, issues of co-operation (or not) will arise. Will Nationalist MPs pit themselves alone against Cameron's crew, or find some basis for that progressive alliance Sturgeon was after? A similar question now faces Labour.

The SNP owes nothing to Westminster and everything to 50% of the Scottish electorate. That fact should be paramount. The puerile vilification of the party - or "the Scots" generally - during the election campaign means there is no obligation on Angus Robertson's group to play nice. The Commons offers plenty of scope for guerilla tactics.

You can only justifiably pursue those, however, if you are sure of two things. First, is it what half the voters wanted when they employed you to shake up the London parliament? Secondly, does it amount to "speaking for Scotland"? Sturgeon has made the point more than once. If you say you are representing the country, that means representing the other 50%, the people who did not vote SNP on May 7, as well as those who gave you their trust. There will be few thanks in that.

For some issues - Europe, human rights, Trident - Nationalist instincts will suffice. Tory arrogance will meanwhile be as helpful as ever. Tearing a hole in the Human Rights Act and pretending to plug the void with a spurious Bill of Rights might appeal to the bluffers and buffers of the Telegraph, but it will not help Cameron overcome the Scotland Act, or - above all - the Good Friday Agreement. The SNP's job will be to expose the new government as cavalier and inept.

It will be slow work, however, while Cameron races to beat the clock. For at least a couple of years, Robertson and his group will engage in the kind of war of attrition that will set few pulses racing among voters at home. Among some who voted SNP, hopes are as high as they are unrealistic. Much - though few seem clear as to what, exactly - is expected. But for as long as there are 331 individuals prepared to call themselves Tory MPs, the majority will prevail.

So who'll open the book on the first Conservative scandal? How about by-elections? There were 21 of those in the last parliament, a half a dozen resulting from the passing of MPs, five from problems in the coalition parties. What of rebellions among Cameron's backbenchers, the rational types who understand perfectly well that the Government has a slim majority and cannot call a snap general election? After eight losses, fun ensues.

When that moment is reached, as reached it will be, the SNP 56 will be in the position Sturgeon hoped to achieve with her campaign overtures to Miliband. There will be influence; there might be real power. Neither will resolve the inherent difficulties for Nationalists in a Unionist parliament, but those will be as nothing to the problems posed for Cameron.

No doubt he has seen it coming. Whether there is much he can do is another matter entirely. Some foxes don't stay shot.