The Tottenham MP criticised Mr Corbyn’s policy of staying neutral on “the biggest issue of the delay” as “triangulation” and claimed that Labour had lost its “moral authority” because of the leadership’s failure to tackle antisemitism.
Mr Lammy said he would decide over the Christmas period whether to enter the leadership contest, which is expected to formally begin in early January.
He would join a contested field that already includes Emily Thornberry, the shadow foreign secretary, and Clive Lewis, the Treasury minister. Sir Keir Starmer, the shadow Brexit secretary, Rebecca Long Bailey, the shadow business secretary, and Lisa Nandy, the Wigan MP, are all expected to stand, while backbenchers Jess Phillips and Yvette Cooper are also thought to be considering a bid.
Mr Lammy described Mr Corbyn, who he has known for decades as a neighbouring north London MP, as “kind, compassionate and thoroughly decent” but said this view of the Labour leader was not shared by voters.
He said: “The leadership’s failure to deal with the stain of antisemitism within the party stripped Labour of moral authority. Jeremy’s triangulation on Brexit left Leavers thinking he was a Remainer and convinced Remainers he supported Leave. His well-reported hostility to institutions such as Nato cemented the public’s distrust.
“It was not Jeremy’s righteous belief in economic justice that lost Labour this election; it was his perceived worldview, failure of competence, and mind-boggling decision to abdicate leadership on the biggest issue of the day.”
Laying out what would probably be his pitch for leader, Mr Lammy called for Labour to promote “civic nationalism” to counter what he called Boris Johnson’s “populist, ethnic nationalism”. He accused the prime minister of having “cynically scapegoated migrants” and said Mr Johnson’s previous comments on race “set a very dangerous precedent”.
He said: “A new tribalism has gripped the UK. However, recent surveys show that on the most fundamental issues – climate change; equal pay and the right of women to have careers; faith in science and scientists; the NHS – we are not divided. On these issues our collective views are converging, and even heading towards a consensus.
“We need a politics that reflects that. The alternative to Johnson’s ethnic nationalism that Labour should offer is a civic nationalism. Rather than basing national pride on biological heritage, skin colour or religion, civic nationalism says we can unite around shared values and institutions.”
Mr Lammy, who served as a minister under Tony Blair and later stood to be Labour’s candidate for Mayor of London, laid out a series of policies that he said would foster civic duty, including setting up a citizens’ assembly to draw up a new written constitution, introducing a proportional voting system, trialling universal basic income and looking at making national civic service compulsory for young people.
Turning to the question of whether he will run for leader, he added: “As for which Labour figure I believe is best-placed to lead this hopeful vision, I will consider that over Christmas.”