Why don’t voters believe that he’s telling the truth?

This single line of data from the Populus poll for February could point to the first big challenge for Brown in the post-Blair world.

For if the Yates inquiry does lead to charges then the line-up of opposition attack dogs – from the Tories to the Lib Dems, the SNP and PC – will have no real interest in Blair himself. He’s yesterday’s man and toast.

The big target will be Gordon and they will try inflict as much damage as possible as he takes over. What better than to try to link him with the affair that is blighting the final period of the Blair era? What exactly did Gordon know and can his denials be believed?

These poll responses suggest that an attack on the Brown line that he had no knowledge would resonate with voters. With getting on for two out of every three Labour supporters saying that the Chancellor must have been aware shows the scale of the challenge.

The great hope for Labour as the seriousness of the investigation has become more apparent is that Tony would be out of the picture soon and Gordon would be able to present himself as the squeaky clean new broom.

But will he? The idea that as a key member of Labour’s campaign team in the run-up to 05/05/05 he did not ask where the millions of pounds of new money were coming from always seemed a touch implausible – but Gordon is the master of not being there to get the blame whenever anything has gone wrong.

The issue here will not be whether Gordon knew or not – but how he handles the onslaught. Will he appear rattled and shaken? Or will he sound convincing and manage to move on to the agenda he has been waiting for a decade and a half to implement?

A key factor might be whether Blair will help and back up the Brown story? Whatever the Brown denial is going to be subject to the most intense scrutiny and it is this that will determine the size and the sustainability of the post-succession Labour bounce in the polls.

In the Labour leadership betting you can still get 0.2/1 which seems good value.

Mike Smithson