Blair, one of the most prominent campaigners for a People's Vote, claims both Britain and the rest of the EU would benefit from the move.
"Europe should prepare for the possibility, now morphing into the near probability, Britain will require an extension of time to the Article 50 process, either to negotiate further or more likely to conduct a new referendum," he will say.
With Prime Minister Theresa May having repeatedly ruled out the prospect, Blair's entreaty seems to be aimed instead at Labour Party head Jeremy Corbyn, and EU member states' leaders. He will suggest it's "bizarre" EU leaders be obliged to facilitate Brexit, a move all of them consider a bad idea.
"Not one believes this course is better than Britain staying in Europe. All of them recognise in years to come this decision will be regretted by future generations. Yet all feel a strange compulsion to carry on. Things do not need to be like this. We have free will. It is past time to exercise it. Brexit is not some form of natural disaster, Brexit is man-made," he will explain.
Moments in Sun
Blair will also attack the various Brexit options that have been proposed by advocates of leaving the EU, suggesting every potential solution "has had its moment in the sun", but then "things have clouded over". The Norway model, he will claim, is just the latest — and all are doomed to fail in his view, as it's so apparent the UK's 45-year-long membership of the EU "has intertwined [the country] with Europe in ways which make disentangling ourselves hideously complex".
In any event, he'll suggest polling shows opinion in the UK is changing, in support of a new referendum — meaning Europe must decide whether to take an historic opportunity and set out a new offer to the British people.
"Such an offer would itself add justification to the case for a People's Vote — but more than that it would show the political leadership of Europe and Britain had listened to the underlying concerns of those who voted Brexit, not disrespecting the concerns but meeting them in a way which is not damaging," he'll conclude.
Blair has long-been a voluble EU advocate, and was a leading supporter of granting membership to countries in Central and Eastern Europe while Prime Minister.
While May managed to hang on to her leadership in a 'no confidence' vote, the Conservative party remains utterly divided over the issue of Brexit, with reports suggesting some MPs from the European Research Group, a Brexiteer faction, are threatening to go "on strike" until there's a change of leader. The MPs may fail to vote in favor of some legislation, to prove May cannot command a majority in the Commons.