Tony Blair will hit out at Jeremy Corbyn's "abject refusal" to lead the UK "out of the Brexit nightmare".
The former Prime Minister will say it is "gut-wrenching" that Labour is not leading the call for a second referendum.
And he will condemn the "stupidity" of the "far left" for denigrating the record of the New Labour years in Government.
In a speech in London, Mr Blair will argue that left-wing populism is not the answer to populism on the right and instead the "progressive centre" must recognise and address the anxieties which have fuelled the phenomenon.
On Brexit, Mr Blair will repeat his call for a second referendum because Theresa May's proposals - "Brexit in name but tied still to Europe in reality" - will disappoint those on both sides.
"Whatever the people voted for, they didn't vote for this," he will say.
"I know it is said a new vote of the people will also divide.
"But a reconsideration in the light of all we now know, accepted by all as the final word, especially if accompanied by a new willingness on the part of Europe's leadership and Britain's to deal with the reasons for the Brexit decision, is the only hope of unity in the future.
"It is frankly gut-wrenching that this call is not being led by Labour as it should be."
In a defence of his record, Mr Blair will say: "The denigration of the Labour Party record in government and its designation by the far left as 'neo-liberal' is one of the most absurd and self-defeating caricatures of modern political history.
"The Labour Party has paid, but more importantly the country has paid, a heavy price for this stupidity.
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"It has undermined the achievements of the party in government. It has weakened the Labour Party's ability to win by depriving it of a unifying message which can reach the centre ground and led to the abject refusal of the Labour leadership to lead the country out of the Brexit nightmare."
In pointed remarks about Mr Corbyn's leadership, the former premier will say populist parties on the left "seldom win power".
Summing up the current position, he will add: "In Britain, we have a Government which is in complete disarray making a mess of the most significant decision this country has taken since the war.
"Yet the Labour Party is barely ahead in the polls and its leadership's ratings languish well behind those of the Prime Minister, who herself faces daily speculation about her position and is highly unlikely to lead them into the next election."
