I’ve just updated my Poll of Polls for polls up to 15-01-15 and it can be found here. Above is the updated graph showing the weekly movement in the Poll of Polls.
I’ve added an extra line that gives the change in the Labour lead. This is the green dotted line, and the axis for this line is on the right.
If you want to download the spreadsheet that did this analysis go here. If you want to understand the methodology behind the “Poll of Polls” click here and scroll down to the bit that gives the description.