A YouGov/The Sun survey on the state of the parties gives Labour a 14-point lead over the Conservatives.
It is the first YouGov poll conducted since Miliband's conference speech and the Labour lead has gone up six points since Wednesday.
Figures also show that the proportion of voters that see Ed Miliband as a strong leader has gone up.
- 31% of those questioned thought Miliband was up to the job of prime minister, compared with 25% before the conference.
- The proportion viewing him as a strong leader rose from 16% to 19%.
However, David Cameron still led by a margin of 31% to 27% when people were asked who would be the best PM.