Labour's new leader in Scotland, Jim Murphy, has done much to command the headlines recently with his interventions on fracking, top rate tax and rail nationalisation.

But that isn't so far translating into an real movement in the opinion polls. The SNP's 20 point lead, established in the months following the referendum, is holding.

If they return up to 40 MPs to Westminster, the Scottish National Party must become a key player in any coalition negotiations to form the next UK government.

On the face of it, a Labour/SNP coalition might look the obvious outcome, since both parties say they oppose austerity, want to stay in Europe and oppose measures such as the bedroom tax. But politics is never obvious.

Labour worries about being portrayed by the Tories in England as being in bed with Alex Salmond - as one of the Conservative Party's recent election adverts indicated. Pressure is being applied by some Scottish Labour MPs for the Labour leader Ed Miliband to rule out any coalition with the SNP so that their message can be that Scottish voters have no choice but to vote Labour if they want to get the Tories out.

Labour's Ed Balls appeared last week to rule out a coalition with the SNP, but his boss, Ed Miliband on his visit to Scotland was less keen on closing the door. The Labour leader is right not to rule out any cooperation with the SNP. Scottish voters might interpret such a lock out as a sign that Labour would prefer to see the Conservatives remain in power rather than ally with the social democratic SNP.

We are entering a new and increasingly fluid era of British politics. No one can foresee the outcome of the next election clearly, and all the parties should be keeping their options open and their cards close to their chests.

This applies also to the Scottish National Party. Nicola Sturgeon has perhaps been too eager to impose her own "red lines" on any dealing with Labour in Westminster after the general election. She has said she will not sit down unless Labour abandons austerity, gives more powers to Holyrood and halts the renewal of the Trident missile system.

She is right to demand devolution max - full home rule - since this is clearly the settled will of most Scottish voters. And she is right to call for more Keynesian economic policies from Labour, which should be pursuing them anyway.

However, while the Sunday Herald agrees that Trident is an abhorrent and unlawful weapon of mass destruction, is it wise at this stage to rule out any post-election talks with Labour unless its replacement is ruled out?

The SNP must remember the fate of the Scottish Liberal Democrats who refused even to discuss a coalition in Holyrood after 2007 unless the SNP dropped its policy of a referendum on independence. The LibDems never recovered from that bizarre act of self-destructive sectarianism.

Politics is the art of compromise, as Syriza has demonstrated in Greece by going into coalition with the right wing Independent Greek party.

The SNP and Labour should resist lapsing back into tribalism. Keep minds, and options open. For the sake of Scotland, if nothing else.