The Shadow Business Secretary said steel is part of “our key strategic infrastructure” and jobs should be kept safe “whatever happens”.
Liberty Steel, Britain’s third-largest steelmaker, is under threat after its parent company’s main lender went into administration.
Specialist bank, Greensill Capital was the main lender to Sanjeev Gupta’s GFG Alliance which includes Liberty Steel – the owner of 11 steel plants across the UK.
Some 5,000 people work for Liberty Steel in the UK, with sites across England, Wales and Scotland, including Newport, Hartlepool, Scunthorpe and Rotherham.
This month, around 180 workers at the Rotherham site were put on furlough, while 660 staff members were told they might not be able to return to work until 14 April.
Mr Miliband told the BBC that the situation at Liberty Steel is “urgent” and “worrying” adding that “nothing should be off the table” when considering plans to save the company, including public financing.
He said: “These are crucial jobs for communities up and down this country.
“Let’s hope that Liberty Steel can find the refinancing that it’s looking for but the Government needs a Plan B to make sure whatever happens, these jobs are saved.
“If there’s one lesson we learned from this pandemic it’s that our strategic infrastructure, our resilience really matters. And steel is a key part of our strategic infrastructure and resilience.
“We cannot afford to let these jobs go. Government has got to make sure it doesn’t happen.”
Mr Miliband’s comments come days after Business Secretary Kwasi Kwarteng said he held “constructive” talks with union leaders to discuss Liberty Steel’s future.
He tweeted on Friday: “I continue to monitor developments very closely and work to build a strong, sustainable steel sector in the UK.”