Can a party founded on the principle of independence work for the benefit of all in a UK institution? Of course they can and the Nats have a history of doing just that in the Scottish Parliament which is of course itself a UK insitution. And during their first term they worked with other parties for the whole of their term as they were a minority administration so they arguably have more form on that than any of the UK wide parties.

And remember they aren't suggesting a coalition (Sturgeon herself said that would be unlikely) and are not looking for gvt positions. They simply said that they could work with Labour on an issue by issue basis. In other words there are some issues where they wouldn't back the gvt. Just as there were some things they couldn't go ahead with in their first term at Holyrood as they were a minority.

The line taken by the London media seems to be that they would only be at Westminster to mischief make - which is an absurd line to take as there is no history to back that up.

They could well look for some things from Labour. Some which are achievable for instance having Ed Miliband look for the Vow on Scotland's constitutional future to be upheld. Other things are unlikely to be agreed - like the scrapping of Trident's upgrade. There would be no benfit of the SNP even thinking about voting against Labour on a confidence vote over that. It wouldn't be logical as the Tories are even more in favour of the upgrade. Again from their own history in gvt the Nats are used to getting what they can and not getting all they want!

As to what would they give to benefit the UK as a whole! Well that depends on your viewpoint. If you are right of centre then I imagine you'd think the Nats have nothing to give. If you are left of centre then they may well be espousing ideas that you agree with. But again remember they are not particularly looking to be in gvt anyway!!