PoliticsHome has a poll that confirms that voters minds are made up. Even if the economy improves it will make little difference to Labour's prospects:
What would be an interesting question to have answered, and it would certainly focus the minds of Labour MPs, is this. If the economy improves and Labour change their leader, would you be more or less likely to vote Labour?
After the Norwich North by-election some bright young thing will start to ask the right question.