Andrew Lansley is under cross-party pressure to publish a secret report on the likely impact of his controversial reforms.
Senior Liberal Democrat Baroness Williams of Crosby joined with the Opposition in demanding the release of the Department of Health’s own strategic risk assessment of the plans.
It follows a ruling last week by information commissioner Christopher Graham that ministers were wrong to keep the document under wraps.
Opposition health spokeswoman Baroness Thornton raised the ruling as peers resumed committee-stage debate on the Health and Social Care Bill.
She said Labour had asked a year ago for publication of the risk register, which set out “key risks” and an assessment of the potential impact on the implementation of the bill through its transition period.
“This information is completely pertinent to further consideration of the bill,” she said.
In his “damning judgment”, Mr Graham had said the DoH must disclose the information within 35 days.
“Were the health secretary to wait until the last possible minute, this would take us near the very end of our committee stage on this bill.”
Lady Thornton urged ministers to make the information available “as soon as possible” and certainly before further consideration of the measure on Wednesday.
Lady Williams said she hoped ministers would give “very careful consideration” to Lady Thornton’s request, insisting it could help to “enrich the debate very substantially”.
She added: “I would plead with the minister on behalf of these benches whether the department could not release these documents as quickly as possible.”
Health minister Earl Howe said there would be public interest in the contents of the risk register but this needed to be balanced with public interest in preserving the ability of officials to freely discuss options before they were fully evaluated.
He warned that disclosure may “deter candid discussions”, which could in turn impact on the quality of decision-making.
“We are currently considering the decision notice from the information commissioner,” he said.
“We have to respond by 6 December and we intend to meet that deadline. Unfortunately I cannot go beyond that commitment today.”