Gordon Brown should, oddly enough, feel reassured. He should know by now that voters are not listening to him. But as important is that none of his possible successors scores with the public either.

Not only is there no assassin, such as Geoffrey Howe or Michael Heseltine against Margaret Thatcher in 1990, but there is no obvious replacement, as Michael Howard was to Iain Duncan Smith in 2003.

The problem with assessing the alternative leaders is that few people know who they are, apart from exceptions like Mr Brown last year. So conventional quantitative polling can only compare relative unknowns. The advantage of the Populus Message Meter, measuring instant reactions, is that people can see politicians in action. By definition, the groups are so small that it is impossible to produce a representative sample. But immediate responses and, even more, later comments in discussion can provide vivid insights. This was shown three years ago when a similar exercise carried out by Frank Luntz, an American pollster, for BBC Newsnight showed David Cameron trouncing his rivals.

Voters do not like the way politicians normally perform, particularly defending an unpopular government. Alan Johnson had the added disadvantage of appearing after a Labour by-election defeat. The politician label also damaged David Miliband and Ed Balls.

By contrast, Jon Cruddas benefited from criticising the Government. And, as he showed in his strong performance in last year’s deputy leadership election, his appeal is because he is not part of the current top team. That would also be a very strong card in any future party election, either before or after the next general election.

The most intriguing winner is James Purnell, who offers freshness and vision. He is not likely to run in any early leadership election. However, if Labour is beaten, there could be a strong backlash against someone as closely associated with a Blairite approach as he has been.

If the exercise is only negative good news for Mr Brown on showing the weakness of his rivals, it also shows the demand for candour about Labour’s past mistakes and ability to offer a clear sense of direction now. That sounds a good brief for Mr Brown’s conference speech in 11 days’ time. In effectively launching the energy-saving package on Thursday, he may have won some breathing space. It may be only a respite.

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