Downing Street has admitted a health minister used private emails for government business despite denying it 24 hours earlier, but defended Lord Bethell, saying he had abided by the guidance.

Bethell, a close ally of the former health secretary Matt Hancock, defended his use of email on Tuesday. “In terms of the use of private email can I just reassure members that I have read the ministerial code, I have signed the ministerial code and I seek to uphold it in everything I do,” he told the House of Lords.

Boris Johnson’s spokesman said the use of personal emails to conduct government business was acceptable if the information was copied to an official account.

“The guidance on using private email addresses is published online. Ministers are able to use various forms of communication as long as they take heed of the guidance that is published,” the spokesman said.

“The guidance itself says those receiving communications should consider if information contained in it is substantive discussions or decisions generated in the course of conducting government business and, if so, take steps to ensure the relevant information is acceptable, for example by copying it to a government email address.”

The comments contradicted the defence No 10 made on Monday, when the spokesman said “both the former health secretary and Lord Bethell understand the rules around personal email usage and only ever conducted government business through their departmental email addresses”.

Bethell, who oversaw the award of Covid contracts, has faced calls for his resignation over his use of private email and his sponsorship of a parliamentary pass for Hancock’s aide Gina Coladangelo, with whom the former health secretary had an affair.

On Monday, the Guardian revealed that a number of emails were copied into Bethell’s private email account. His address was copied into at least four official exchanges relating to a businessman who was attempting to get government contracts during the pandemic.

In April 2020, the businessman had approached his MP, Oliver Dowden, as he believed his firm’s testing kits were cheaper than those being bought by the government.

Andrew Feldman, the former Conservative party chairman who had been brought into the government to advise on its approach to the pandemic, passed on the matter to a number of officials, copying in a private email address belonging to Bethell.

Later that day, a Department of Health and Social Care official (DHSC) circulated another email to his colleagues, again copying in the private email address belonging to Bethell.

The emails were obtained by the Good Law Project, which has launched a series of legal challenges over the government’s handling of contracts during the pandemic.

Hancock is reported to have routinely used a private account, according to minutes of an official meeting at the DHSC seen by the Sunday Times. The minutes said Hancock was only dealing with his private office “via Gmail account” and said he did not have a departmental inbox.

The minutes, which were to discuss a Good Law Project legal challenge over government contracts for faulty tests, also say that Bethell “routinely uses his personal inbox and the majority of [approvals for contracts] would have been initiated from this inbox”.

Angela Rayner, Labour’s shadow chancellor for the Duchy of Lancaster, said Bethell should publish his correspondence from his private account.

“The government must immediately publish all of Lord Bethell’s private email correspondence regarding government contracts, and his private emails must be secured for the public inquiry,” she said.

“Lord Bethell should be sacked by the prime minister after the prime minister’s shameful failure to show any leadership or judgment by sacking Matt Hancock.

“We need a full independent inquiry to get to the bottom of the use of private emails by government ministers to uncover any more dodgy dealings, protect our national security and ensure ministers cannot hide from scrutiny and the public inquiry.”