Labour former leader Neil Kinnock today backed Gordon Brown ahead of his final conference speech before the General Election, hailing him as a "definite winner".
But he said the Prime Minister would not make the "huge change" in his disposition some have called for.
Instead, he would be concentrating on the "fundamental essentials".
Voters would prefer to see a "focused" and "grave" leader as opposed to a "wonderful communicator" who was a "lightweight", he claimed.
Lord Kinnock revealed that in conversations with Mr Brown over the years he had urged him to be "more himself" and return to being a "fleet-footed, highly-articulate, wonderfully lucid and forceful" politician.
But Mr Brown had resisted "loosening up", partly because of his, then, position as Chancellor and also because he believed it would hand ammunition to his critics if he met their demands that he change.
Lord Kinnock, who led Labour from 1983 to 1992, told BBC Radio 4's Today programme: "He is not going to make a huge change in his disposition publicly or privately. He wants, as he says repeatedly, to concentrate on the fundamental essentials of the job in hand and that is what he is doing."
He added: "If people think about it they would rather have the real, grave, concentrating, focused, determined thing that is bringing about the absolutely vital changes in the management of the world economy and the actions to combat climate change than have someone who is a wonderful communicator and a great entertainer but is lightweight."
Lord Kinnock urged Mr Brown not to give in to those in his party and outside who wished to see him step down. Asked what a leader had to do when he was increasingly unpopular, he said: "You keep on fighting, obviously. When the election date is closing to take any other course would be indefensible because you have got an obligation to the country, you have got an obligation to your party and you have got an obligation to your own conscience and your own sense of judgment to keep on doing it."
Lord Kinnock, referring to Mr Brown's loss of sight in one eye following a rugby accident as a teenager, said the "character-forming experience" gave him a "maturity, a sense of direction" that many politicians did not have.
But he could not explain why the trauma, which he said equipped the premier with a "certain strength", did not endear him with voters.
"It is very difficult to explain. I think it has a great deal to do with the way in which, almost from the outset, Gordon has been represented by most of the media in the most vindictive way."
Lord Kinnock said Mr Brown and the Labour Party had to get the public to focus on what really mattered: "the survival of the planet and the return to sustainable growth and employment".
He added: "On those grounds, if people concentrate there, Gordon Brown is a definite winner."Reuse content