Sort of continuing

Tuyrnout will be key to the election.

If as Phil notes, Labour would have to lose 78 seats to lose their majority then somewhere around 250,000 voters are going to have to change their vote (all other things being equal from last time. I am aware that this is highly unreasonable, and there is no good cause for thinking the vote last time will affect the vote this, save that previously people have demonstrated an unwillingness to change their minds dramatically at elections.) That is, the 78 most marginal Labour seats have a combined majority of 252,265.

Now, assuming all other things are equal, then the Tories would need to gain half of that number plus one in each seat. That is a total of 126,211 votes. That is an average of 1,618 votes per seat. In the scheme of things not a huge number - although if they got precisely that number that would only get them 35 of the total of seats. To get the 78th seats, for example, they would need 2,978, which, out of an electorate of 60,000 or so per seat is not mean shakes, but does not represent that astounding a figure.

That is, the real figures, not the percentages, show how slender Labour's lead is, and how, without the Tory vote overtaking Labour's they could destroy it's majority. But that would just lead to PR.

But, there is more, the real formula must be that the Tories should need:
(Labour Majority - Abstentions)/2+1 - where any vote for a party other than the one in second place counts as an abstention. Thus, in effect, every two abstentions equals one vote for the Tories.

Hence why Labour is discouraging tactical voting, hence why the fear a low turnout, and hence the reports at Harry's Place.

As it goes, Strategic Voter gives previous example of electoral volatility brought on by small shifts in voting. I'd only add, that these battleground marginal voters amount to less than the number who voted for various state-capitalist and reformist parties with Socialist in ther name at the last election. Accidents of geography seem to place a huge part in this story.