A hung parliament with how many power brokers?

I was struck by the latest opinion poll in the Guardian, not by the Con/Lab/LD results, which were much the same as they've been for some time now, but by the figure for the SNP and Plaid Cymru.

At 5%, (UK-wide), this was up (from 4.4%, so far from statistically significant) on their results in the Scottish Parliament/National Assembly elections and more than double the result they got in the 2005 General Election.

A simple doubling of their vote shares, with the adjustments of the 3 UK-wide parties based on the opinion poll movement, showed the SNP on 25 seats (up from 6 at the 05 election) and Plaid Cymru on 6 (up from 3 at the 05 election).

Which from the same doubling in vote share is a far better performance for the SNP than for Plaid - a reflection of quite how far behind Labour in Wales (every other party including) Plaid come in.

But also shows that, on a slightly smaller swing to the Tories, it won't be just the LibDems that may have a choice to make about supporting a government, but Plaid and the SNP. Will this effect how either Labour or the Conservatives will approach the issues of an independence referendum for Scotland or full powers for the National Assembly in Wales?

In one way, the above isn't a fair comparison, doubling vote share is only a uniform swing if you start from the same point. So, taking Plaid from c12% to c24% is a smaller gain than the SNP from c17% to c34%. But that 10% difference doesn't account for why the Scots can quadruple their seat numbers, and the Welsh only double them (add on that extra 10% or so to Plaid and they reach 10 seats). Move the Plaid gain to a (quite ridiculous) quadrupling of the vote, and they end up with 18 seats, more akin to the gain that their Scottish counterparts make.

So, two conclusions from this. Firstly, that a hung parliament could easily feature the SNP and Plaid Cymru as power brokers, just as much as it does the LibDems or the Northern Irish parties. Secondly, that Plaid have to do so much better than the SNP to make the same sort of breakthrough.