Labour has called for an inquiry into whether lobbyists employed by the government during the Covid response benefited from privileged information.
It comes after the Sunday Times reported that one lobbyist, who had worked on NHS Test and Trace, went on to share information with clients.
After leaving his post he reportedly shared sensitive lockdown information.
The Department of Health and Social Care said all conflicts of interests were declared before he was appointed.
But Labour's deputy leader, Angela Rayner, has said the Sunday Times' allegation was "the latest in a long line of revelations regarding businesses and individuals with close links to the Conservative Party that have adversely affected public trust during this pandemic".
According to the Sunday Times newspaper, the chairman of lobbying firm Portland Communications, George Pascoe-Watson, was hired to work on NHS Test and Trace in April. The DHSC confirmed it had hired Mr Pascoe-Watson for six months as an unpaid adviser.
The Sunday Times claimed that Mr Pascoe-Watson took part in meetings with Health Secretary Matt Hancock and Test and Trace chief Dido Harding over how to communicate policies to the public.
It alleged that after Mr Pascoe-Watson - who represents pharmaceutical companies, weapons manufacturers and banks - left the post on 7 October, he passed information onto paying clients ahead of the second national lockdown announcement at the end of October.
Mr Pascoe-Watson confirmed he emailed clients in the days after he left, but said: "The information shared with clients on 15 and 29 October was in no way connected to the Test and Trace calls, in which I was no longer a participant."
He added to the Guardian that the information had come from "multiple conversations had by our consultants".
After the story was published, Labour's deputy leader, Angela Rayner, wrote to Cabinet Secretary Simon Case, demanding an urgent inquiry into "how lobbyists and their clients benefited from this vital information before the public knew".
She said if the allegations were true, information was passed on at a time when "the rest of the country waited anxiously for government announcements about lockdown and whether they could see their families, friends and loved ones".
Ms Rayner added it was "deeply insulting" to the British public and called for the Cabinet Office to "shine a light on this situation in order to maintain public trust" over the hiring of government advisers.
The SNP joined the call for an inquiry, accusing the government of "rampant cronyism".
The party's deputy leader in Westminster, Kirsten Oswald, said: "There must be a public inquiry into the scandalous way that public money, jobs and privileged access have been handed out by the Tory government during this crisis."
A spokesman for the DHSC said: "As part of an unprecedented response to this global pandemic we rightly have drawn on the expertise of a number of private sector partners who provided advice and expertise to assist in the government's vital work.
"This included helping establish the largest diagnostic network in British history and a test and trace system used by tens of millions of people.
"As a result of public and private sector organisations working together at pace, we were able to strengthen our response to the pandemic so we are better prepared for the challenges of the coming months."