His spokesman branded the upper chamber of parliament “absurd” and an “undemocratic anachronism”, as he vowed a Labour government would be committed to scrapping it.
He said new members of the chamber recently appointed by the party only gained their peerages on the basis that they would back abolition in any future vote.
While Mr Corbyn’s desire for an elected upper chamber has been longstanding, the latest intervention comes after a major rebellion by existing Labour peers against his policy direction on the EU single market.
Meanwhile, Theresa May’s spokesman defended the prime minister’s decision to appoint new lords last week, including ex-ministers, despite having previously promised to end the right of former frontbenchers to gain a seat in the chamber.
Speaking on Wednesday, Mr Corbyn’s spokesman said he was clear that the leader wants the Lords scrapped.
He appeared to edge beyond the wording of Labour’s 2017 manifesto, which said an elected upper chamber is desirable, but “in the meantime” the party would focus on reducing the size of the current house.
But Mr Corbyn’s spokesman said: “We’ve made clear, Jeremy has made clear, it was in our manifesto – we want to see the abolition of the House of Lords and its replacement with an elected second chamber.
“That is well past overdue, it’s a basic democratic reform, it must take place.
“It’s absurd that we still have this undemocratic anachronism in the 21st century. When Labour is elected we will carry through that pledge.”
Asked whether he was now going further than the manifesto, he added: “The commitment is clear. And by the way, anyone who is appointed to the House of Lords under existing rules from the Labour party is required to support that.”
Mr Corbyn recently appointed former Labour general secretary Iain McNicol, campaigner Martha Osamor and writer Pauline Bryan to the Lords.
But the strong words from his spokesman also come after more than 80 Labour peers ignored their leader’s will and backed a plan to keep the UK in the EU’s single market.
They helped rebel Tory peers to inflict a defeat on the government over the issue during the passage of Ms May’s EU (Withdrawal) Bill – one of 15 her administration suffered in recent weeks.
Ms May has also recently appointed nine new peers to the Lords. Questioned on how she justified the new commitments, her spokesman said that the overall size of the Lords had reduced during her tenure.
And on appointing ex-ministers, like Peter Lilley and Sir Eric Pickles, he said: “The nominations reflect our determination that the House of Lords should contain people from various walks of life.
“But also people who have expertise that can add to the overall contribution the house makes.”
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