On Wed, 10 Jun 2015 21:26:02 +1000, John Chance wrote:

UKIP supporters can safely be assumed to have actively voted.

Not sure of that. Some of them presumably didnt have anyone in their
electorate to vote for.

UKIP stood in 624 of 650 seats, so that's a fairly minimal number of
potential extra voters. Given that the average UKIP candidate got 6,200
votes, we're talking about a likely extra 160,000 - an extra 0.5% of
votes cast at most.

In practice, I think we can presume that the constituencies they didn't
stand in were ones they would have had significantly less support than
average in.

FWIW, Labour and LD stood in 631, Conservative in 647.