Study based on YouGov MRP poll suggests just 21,215 voters can decide election if they vote tactically to deny the Tories in 30 seats they are currently expected to win.
The prime minister was labelled "Britain's biggest bottlejob" by Piers Morgan as an aide drops the f-bomb live on ITV's Good Morning Britain.
The prime minister refused to look at an image of Jack Williment-Barr sleeping on a pile of coats in an NHS hospital.
The prime minister also refused to actually look at a photograph of Jack Williment-Barr, 4, sleeping on a pile of coats in A&E with suspected pneumonia.
The Tory and Labour leaders went head-to-head for a final time before December 12, with a snap poll giving the PM a 52-48 victory.