So, looking into this data a little more (according to the BBC news feed).
They have asked 23,790 people at 144 polling stations.
The reality is there are 650 seats and 30 odd million voters, how the hell can you take the exit poll seriously??
They have taken the word of the very few people from each polling station who were prepared to tell them who they voted for. That is 165 people at each of the exit polls they surveyed. That is a very small sample and it is very easy to skew the result based on such a small sample size.