Labour is now on 44 per cent, way ahead of the Conservatives on 33.
It is the party's biggest lead since the weeks following its 2005 election victory, and the strongest since Mr Brown took over as leader. Among women voters, the gap is even more dramatic at 16 percentage points.
The findings, in a YouGov survey for Channel Four News, are a shattering blow to David Cameron ahead of his conference in Blackpool next week, which is increasingly being seen as a make-orbreak-test of his leadership.
If repeated at a general election, such a lead would translate into a massive majority of up to 170 - greater than the 165-seat landslide that swept Labour to power in 1997.