Labour has posted a 12-point opinion poll lead over the Tories - its widest margin of advantage in a ComRes survey for more than seven years.
The Opposition gained two points to 43% on a month ago and the Conservatives dropped two to 31%, in the poll conducted for the Independent on Sunday and Sunday Mirror.
It showed the Liberal Democrats static on 10% and Ukip down one on 8%.
More top news
The party's deputy-leader is the sole candidate in the race to succeed Gerry Adams.
A Met Office yellow "be aware" warning for ice is in place across much of Scotland, Northern Ireland and northern England.
Nick Boles warned the PM it was "time to raise your game" and claimed her government "constantly disappoints" in a tweet.