In another major intervention, the former prime minister and pro-Remain cheerleader will repeat his call for another referendum – on the terms of the Brexit deal.
He is also expected to bitterly attack both Theresa May, dismissing her as a Brexit hostage, and Jeremy Corbyn, accusing him of neglecting to lead the fight for the future of Britain.
And, in a Chatham House lecture, Mr Blair will issue a rallying call to pro-Remain Labour and Conservative backbenchers to defy their party leaders and rebel on Brexit.
The former Labour premier, branded the Remainer-in-chief by Brexiteers, is also set to claim the rise of populism in European countries such as Italy risks a return to the 1930s.
On Brexit, Mr Blair will declare We cannot go on like this. I have never been more worried about the future of our country than now, with competing emotions of anxiety and rage.
We have a government whose every move is a calculation not about the interests of the nation, but the internal balance of advantage between the factions of the Conservative party, with the prime minister more a hostage than a leader.
Meanwhile, the leader of the Labour Party neglects to lead the fight here at home over an issue which literally determines the future of Britain and where he could play a decisive role.
Parliament must assert itself because neither government nor opposition can or will.
Then the people must make the final decision, because only they have the right to decide what version of Brexit they want or whether in the light of all they now know they prefer to remain.
Mr Blair claims the present impasse in Brexit negotiations and inside the Cabinet is imperilling the UK’s economy, international standing and alliances with other countries.
Crashing out with no agreement would deal Britain a devastating blow, he will say. We should plan now for the possibility we need to extend the March 2019 deadline.
Presently, we are drifting towards March 2019 with no clear negotiating position, no resolution of the Northern Ireland question, still vaguely hoping Europe will allow us access to the Single Market without abiding by its rules, which it will never do.
And with senior cabinet members openly debating the merits of a negotiating position which ‘threatens’ Europe with a no deal Brexit.
This is the equivalent of holding a negotiation on the top floor of a high rise building and ‘threatening’ to jump out of the window if our demands are not met.
The whole thing has become so protracted that it has numbed our outrage.
Mr Blair’s calls for an extension of the Brexit deadline and a second referendum will be derided by Brexiteers, coming less than 24 hours after the EU (Withdrawal) Bill received royal assent from the Queen – officially becoming law.
But revealing his frustration about the Brexit stalemate, Mr Blair will say I am afraid I get bored with people telling me they’re bored of Brexit.
If it is by consensus the most important decision we have taken as a country since World War Two, then our preoccupation with it must continue until one way or another it is finally decided.
Mr Blair will say the debate on Brexit has naturally focused on the economic fall-out, but the political effect of Britain leaving the EU may be worse.
At a stroke, Britain loses its position in the world’s largest commercial market and biggest political union, he will say. America loses its foremost ally which has often been a bridge between the two sides of the alliance.
Of course, the Brexiteers will argue that Britain can still be the USA’s greatest ally outside the EU. But examine the reality. Since Brexit, is Britain closer to the USA? Is the relationship stronger?
On a global issue, who is the American President calling first on the continent of Europe – the British Prime Minister?
And on populism, Mr Blair says The populist wave upending Western politics shows no sign of abating. Italy proves that.
It is difficult to predict whether we are at the crest of the wave which will soon subside or whether it is still building its momentum. But I fear it is the latter.
He adds Once it is clear the populism isn’t working because, ultimately, it offers only expressions of anger and not effective answers, the populists may double down, alleging that failure is the result of half-heartedness and that only more of the same will work.
Who knows where the dynamic of that scenario takes us. Then the comparisons with the 1930s no longer seem far-fetched.
News Source SkyNews