The final Guardian/ICM poll of 2015 is pretty much as you were, with the Conservatives remaining static on 39% (but still a point ahead of their General Election showing) and Labour up one to now stand on 34% – equally their post-election high.
Top line numbers are:
Liberal Democrats 7%
Plaid Cymru 1%
That Labour stand above their election share is possibly less the result of a commanding leadership performance that has invigorated the Labour masses, but more likely the continued over-statement of Labour in phone polls for sampling reasons. It should be noted that nearly all online polling has Labour hovering around the 30% floor, and although this is only a relatively small variation between methods, it is sufficient to exercise the mind as pollsters (especially us here at ICM) await the findings of the BPC Inquiry in January.
For our part, it is clear that phone polls steadfastly continue to collect too many Labour voters in the raw sample, and the challenge for phone polling is to find a way to overcome the systematic reasons for doing so. The methodological tweaks that we have introduced since the election in part help mitigate this phenomenon by proxy, but have not overcome the core challenge. In our view, attempting to fully solve sampling bias via post-survey adjustment methods is a step too far and lures the unsuspecting pollster into (further) blase confidence.
We will have more to say on our methods in the coming months.