Labour have really been playing nothing but blinders since the manifesto was "leaked" while the Tories have started to trip up.
McDonnell has skilfully managed to turn the narrative of the Tory manifesto into one of cuts for pensioners' fuel tax, and of the Tory manifesto being uncosted, unlike Labour's. The complacent bastards never expected to be held to account for this - and the beauty of it is that it makes it very difficult for the Tories to use the "yes, yes, very well, but how will you PAY for all this....????" argument against Labour's manifesto, as it is now they who are going on TV saying that it isn't necessary for a manifesto to be fully costed.
To top it off, Jamie Oliver is on BBC attacking it for abolishing free school meals, and every other party leader seems to focusing chiefly on attacking the Tories along similar lines. Could the perception that Labour are already out of the game have a "crouching tiger, hidden dragon" effect? The other parties ignore Labour and attack the Tories, and the Tories make mistakes from complacency.
I reckon the gap may narrow to single figures - let's see how the polls look next week.