Pollsters: That UKIP Majority.

In Rochester, the polls showed a UKIP lead over the Tories of between 12% and 15%. This is the first time ever that UKIP support has ever been overestimated by pollsters and started to happen only when it became clear that UKIP would take the seat. I honestly wonder at how much the pollsters get wrong about UKIP. Underestimating the party in order to play it down is one thing but then going the other way to make the UKIP victory rather appear less spectacular is making me profoundly suspicious.
I have known for some weeks what the result was going to be. A UKIP MEP told me that it would be 7% to 8% - a fact that the party has known for a long time. So how is it that UKIP's private polling is so much more in line with reality? - Work it out for yourself!