The British opinion polls are all over the place at the moment, yes. It's very likely that these are not sampling issues, though. British politics is currently

The British opinion polls are all over the place at the moment, yes. It's very likely that these are not sampling issues, though. British politics is currently in a period of realignment with the position of all parties in flux. Election polling relies heavily on turnout modeling: it's not enough to know what people's opinions are to predict elections, but also which of those people are likely to vote. And the different polling companies have very different models for that, and other 'artistic' parts of the modeling which aren't strictly related to their polling sample. It certainly doesn't imply problems for survey research as a whole (though, as I said, there are increasingly long-term challenges to the while edifice).