The SNP would have a bargaining position to start from but they are quite used to getting what they can and not always what they want. So I imagine they'd get by with a measure of what they want rather than risk actually bringing a potential Labour gvt down. I'd think they would insist on full delivery of the Vow re what was promised re more powers for the Scottish parliament. Salmond famously said they'd hold their feet to the fire over that. Labour could hardly say it isn't their policy when Milliband signed up for it and got Gordon Brown to trumpet it.

They would probably see themselves as perhaps influencing Labour economic policy (ie large sections of Labour MPs would agree with the SNP anyway) rather than actually writing it. Rather like the Lib Dems suggest Tory policy is not Lib Dem policy but they had a influence and restrained the Tories a bit. Except even if offered, which it wouldn't be anyway, I don't think the SNP would accept gvt posts. I think they'd much prefer to be seen as a party trying to influence Labour. Try and take some credit where they can and shy away from the blame for unpopular policies.

Likewise they would look for a Labour gvt not to spend billions on the new Trident which may be a step too far for Labour. Don't think that would be a deal buster despite all the rhetoric. The Nats would probably just blame Labour for being intransigent in spending on bombs rather than bairns and say it would be pointless forcing the issue as the alternative Tory gvt supports the renewal anyway. Same re the House of Lords being abolished. SNP policy which would be blamed on Labour if it didn't materialize.

Most of all they wouldn't want to do anything to upset their seemingly massive lead in the Holyrood polls for the next Scottish election. So I think some commentators (mostly Tory) who say they will just come to intentionally cause mayhem are seriously wide of the mark.

Plus it remains to be seen actually how many there will be anyway. Sturgeon is being very coy and reminding people that even 12 or 13 MPs would be a success in that it is more than they've ever had before. They seemingly believe (bar some big sea change) that should get in the 30s perhaps even to 40 seats. If they got 50 or more I'm sure they'd be over the moon but they know that the people suggesting that will happen are talking about a uniform swing across the country - and it doesn't necessarily happen like that. Plus for instance the Electoral Calculus site has for my constituency (which once was solidly Lib Dem) the Nats on 34.8% and the Tories on 32.4% which is well within any margin of error. Yes they have the likelyhood of an SNP win at 52% and the Tories only about 37%. I honestly don't see how they get to that!