Iain Anderson is co-founder of Cicero Group and is an expert in global political risk and economic public policy issues. He has worked for a range of Conservative policymakers. He writes in a personal capacity.

The polling during the past few weeks has continued to give the SNP a commanding lead in Scotland, while a disastrous start to campaigning for Labour across the UK is starting to reduce odds on a the Conservatives being the largest party come May 8.

Last week’s polling by Lord Ashcroft sets a course for the General Election in Scotland which is going to be very difficult for Labour to reverse. Jim Murphy is talented, but there’s just not enough time for him to turn the tide.

None the less, the central narrative among the London commentariat is of a Labour-Liberal Democrat- Green pact. Or of a Tory-DUP-LibDem pact. But no-one is starting to call what might become the most likely outcome: a Conservative-SNP deal – if the SNP secures well over 35 seats.

This side of May 7 – the SNP are steadfastly sticking to their line that there is no deal to do with a Tory government in Westminster. A canny campaigning move.

But don’t forget there were ongoing deals on finance bills between the Scottish Conservatives and the SNP from 2007 onwards which kept Alex Salmond in office running his minority Government.

It is easy to see why the SNP would not want to play into Labour’s hands by muting a deal with the ‘hated Tories’.  But there is already more potential for a deal here than meets the eye.

The Scottish Conservatives’ Strathclyde Commission was the most radical set of options produced by any of the unionist parties in advance of the Independence Referendum last year.

Its central idea – full devolution of fiscal powers on income taxes – made Labour and the Liberal Democrats reform plans pale into insignificance. Forget the Vow or the Vow Plus: Strathclyde’s ideas gave Ruth Davidson and the Scottish Tories the clearest campaign message on the Unionist side last year. In ways, it went even further than the Smith Commission itself.

While the concept of EVEL works for, say, the Daily Mail brilliantly, it will only serve to benefit the SNP during the campaign. It is already doing so. And Labour remains without an effective answer to the West Lothian question. As Daniel Hannan argued on these pages recently, a federal UK now makes some considerable sense. This big idea should make its way into the Conservative manifesto.

But I fear it won’t. If Devo Max had been on the ballot paper in September last year, it would have won hands down. That said, I think it is increasingly the choice that may keep David Cameron in Downing Street. And I think we had better start preparing for that.