Here’s a funny thing. Polls that carry out fieldwork online are 3-9 points more favourable to the “big 2” than phone surveys
The big methodology difference is in sampling. The phone firms used randomised dialling and theoretically anybody with a landline, and now mobile, can be included.
Online polls are generally carried out amongst members of a polling panel who perhaps are slightly different from the electorate as a whole in they’ve signed up in the first place and are doing the survey for money.
It was only when I was looking through recent findings from the different firms that I found the split featured in the chart above.