The shadow chancellor, Rachel Reeves, then stood in for the Labour leader to respond to Rishi Sunak’s Budget statement.
Sir Keir has had to self-isolate on four separate occasions since March 2020 under the now-expired Covid restrictions – after coming into contact with someone who had tested positive.
During the summer, the Labour leader was forced to abandon a summer tour of the Midlands, as part of a series of conversations across the country with voters who abandoned the party at the last general election.
Mr Miliband, who resigned as leader of the party immediately after his election loss to David Cameron in 2015, was greeted by ironic cheers from Tory MPs when he stood up in the Commons chamber.
He joked to MPs: “Just like the old days.
“I just want to reassure both sides of the House it’s one time only,” he added.
Mr Miliband used the session ahead of the Budget to criticise the government for cutting overseas aid while simultaneously lobbying nations for $100bn of climate finance for poorer nations ahead of the critical climate summit – Cop26 – in Glasgow.
“We all need the vital Cop26 summit in Glasgow to deliver next week because failing to limit global warming to 1.5 degrees will have devastating consequences for our planet and that is shared across this House,” Mr Miliband told MPs.
“Does the prime minister agree that to keep that goal of 1.5 degrees alive we need to roughly halve global emissions in this decisive decade?”
Mr Johnson replied: “It is of course correct that Cop26 is both unbelievably important for our planet but also very difficult and it’s in the balance.”
During prime minister’s questions, the chancellor, Rishi Sunak, and the justice secretary, Dominic Raab, were among senior Tory MPs wearing masks in the chamber – after the health secretary, Sajid Javid, urged politicians to set an example.