JonnoH - that's why they put this note to say its not reliable:
"How Accurate is the Prediction?
The Calculator is based on applying a uniform swings to the results from 2010. This is an unrealistic assumption, as in real life, the swing varies from seat to seat. The calculator can be used as a guide as to what would occur if a swing was uniform, but the predictions for individual seats should be treated with caution."
