THE CORRECT ANSWER
Nate Silver is probably the world’s leading analyst of polls.  His opinion, stated yesterday, is that

–“The World May Have A Polling Problem,” Silver asserted. “In fact, it’s become harder to find an election in which the polls did all that well.” Silver went on to cite four examples where the polls had failed to provide an accurate forecast of the election outcome: the Scottish independence referendum, the 2014 U.S. midterms, the Israeli legislative elections, and even the 2012 U.S. presidential election, where “Obama beat the final polling averages by about 3 points nationwide.”
“There are lots of reasons to worry about the state of the polling industry,” Silver concluded, citing a range of factors. “There may be more difficult times ahead for the polling industry.”—

What he is saying is that there is conscious, and increasing bias in the polls, and that he will be able to use forensic statistics to determine who is biasing polls by how much.

The purpose of polling whenever results are reported is to manufacture opinion.

https://www.quora.com/Why-were-all-the-polls-in-the-2015-UK-general-election-so-different-from-the-results