Jeremy Corbyn will miss a House of Commons vote on whether to order a fresh probe into allegations that Tony Blair misled Parliament over the Iraq War.
Wednesday’s vote has split the Labour parliamentary party, with the Shadow Cabinet facing down calls by backbenchers for all MPs to be ordered to oppose it.
Instead, Labour MPs face only a one-line whip – not a strict three-line whip – which means it is not essential to them to attend and vote.
Some Labour MPs were furious, believing their party should have been ready to take disciplinary action against any MP failing to reject the motion, drawn up by the SNP.
It demands a new investigation by a Parliamentary committee that could even result in Mr Blair being stripped of his Privy Council membership.
The Independent has learned that Mr Corbyn will miss the vote altogether, because he is “committed elsewhere”.
In July, when the Chilcot report was published, Mr Corbyn told Parliament that the evidence on Iraq's weapons of mass destruction was “flimsy and confected”.
And he said: “We now know that the House was misled in the run-up to the war and the House must now decide how to deal with it 13 years later, just as all those who took the decisions laid bare in the Chilcot Report must face up to the consequences of their actions, whatever they may be.”
The September 2002 dossier, which warned of weapons that could be made ready in 45 minutes, was “the only most notorious of many deceptions”, he added.
It was suggested at the weekend that some “senior” Labour MPs will vote with the alliance of the SNP, Plaid Cymru and Green party co-leader Caroline Lucas.
But several former ministers in the Blair and Brown government are expected to turn out to defend the former Prime Minister from the charge that he knowingly misled Parliament.
Ms Lucas piled pressure on Mr Corbyn to attend the debate and vote for the investigation, saying he had opposed the war and had “called for those who led us into the disastrous conflict to be held to account”.
She added: “To now back away from taking the action to match their words would be deeply disappointing and would damage the prospects of learning serious lessons from what went wrong in the run up to war in Iraq.
“Labour should not shy away from their role in Iraq, and shouldn’t be protecting Blair and his allies from being held to account for the actions which led this country into military intervention.”
The debate is expected to focus on revelations that the Chilcot inquiry was designed by senior civil servants to “avoid blame” and reduce the risk that individuals and the government could face legal proceedings.
Documents released under freedom of information laws, also showed that officials involved in planning the inquiry - including current Cabinet Secretary Sir Jeremy Heywood - were involved in the events that led to war.
Labour refused to comment about whipping arrangements, but one source said the Shadow Cabinet had decided “to oppose” the SNP motion.