What can the "feeble 56", as some are calling the SNP MPs, actually achieve?

They don't hold the balance of power; they are pariahs in the eyes if the UK press; they can't abolish Trident; and they don't even seem to want full fiscal autonomy any more.

Are they just going to collect their salaries and jeer at the Tories? An inexperienced rabble of student revolutionaries and has-been SNP stalwarts who don't really want to be part of the Westminster at all?

No, I don't think so. The SNP MPs have a chance to exert significant influence in the Westminster system. Just being there is a large part of it. They are the third largest party by far in the UK legislature.

SNP MPs will get to move debates, contribute amendments to bills, chair select committees. They are part of the Westminster machine and will be represented on the bodies that organise the business of the House.

Parliament is largely theatre and the fact that Scotland is now almost entirely represented by SNP MPs dramatises the new constitutional divide.

We will see the new Scottish Secretary, David Mundell standing alone against 58 opposition MPs at what will now be known as "Panda Question Time" in the Commons.

Lots of English Conservative MPs with dubious Scottish connections will have to be drafted in to support him. But it is not possible to rule when no one takes you seriously.

Government is not just about numbers; it is also about winning the argument. David Cameron probably never thought he would be in a position to impose English Votes for English Laws (Evel), but now he has no excuse.

Evel may unite all 319 opposition MPs against the move to lock opposition MPs out of votes on nominally "English" bills.

Students of history know that three Irish Home Rule bills failed to resolve the conundrum of what exactly an "English" bill is in a unitary parliament.

The rumours that David Cameron was going to offer full fiscal responsibility were just that, but he is going to have to negotiate further devolution of powers.

Westminster commentators and MPs will discover that the SNP has not given up on devo max and will be arguing for a rapid extension of Holyrood's powers. If some Tory back-benchers also want to aid the SNP by arguing for full fiscal autonomy, then so be it.

All bar one of Scotland's MPs will support moves to introduce federalism, reform of the House of Lords and English devolution. That will be a challenge to those constitutional reformers in and out of Westminster who have talked about this for decades but who have never done anything about it.

The 57 anti-nuclear MPs cannot abolish Trident. But the fact that all but two of Scotland's elected representatives oppose this weapons system is a very strong argument against renewal.

It will make senior civil servants and military figures begin to wonder. Is it really sensible, militarily or democratically, to impose this weapons system on a country where almost all of its elected representatives are opposed to it?

Measures like the attempt to abolish the Human Rights Act (HRA) will be challenged by Scottish MPs. They will argue, correctly, that it is unconstitutional to abolish the HRA without the agreement of the Scottish Parliament under the Sewel convention.

John Whittingdale, the new Conservative Culture Secretary, is seeking to alter the BBC in fundamental ways. The SNP MPs will have their own take on this and will argue for the devolution of broadcasting to the Scottish Parliament.

On Europe, the 56 might even find themselves siding with David Cameron against his own Eurosceptics. Cameron has a tiny majority of 10. He only need lose the votes of five Tory MPs and it disappears.

The 56 are not teenage rebels. People like George Kerevan, the MP for East Lothian, have wide experience of business, media and local government.

Tommy Sheppard of Edinburgh East hasn't just run a chain of successful comedy clubs, he was assistant secretary of the Labour Party and is a former deputy leader of Hackney council.

Philippa Whitford is a surgeon, Michelle Thomson was in charge of Business for Scotland.

There isn't an Oxbridge graduate or a policy wonk among them. Of course, they will make a lot of mistakes and the SNP group may fail to cohere.

But these are interesting times; the first time since I left Westminster in 1999 that I almost miss the place.