Tory minister Robert Jenrick has been referred to Parliament's sleaze watchdog over 'cash for favours' claims.
It came as Boris Johnson was under increasing pressure to reveal what contact he has had with billionaire mogul Richard Desmond - whose East London property deal is at the centre of the row - since he became Prime Minister.
Labour said "fresh questions" about the case forced them to report Mr Jenrick to the Parliamentary Commissioner for Standards to investigate a potential breach of the MPs' code.
The PM has resisted launching a full government inquiry into Mr Jenrick's handling of the Westferry Printworks planning appeal.
There's no suggestion of wrongdoing on Mr Desmond's part.
Steve Reed, Labour’s Shadow Communities and Local Government Secretary, said: “The Prime Minister can’t just sweep this issue under the carpet."
He added: “The Prime Minister has yet again shown woefully poor judgment by not referring clear breaches of the Ministerial Code to the Cabinet Secretary and he must now come clean himself about his own involvement in this case.
“The Government must publish all the remaining secret documents in this case to show the public what Mr Jenrick and the Prime Minister were really up to and prove that this is not the start of a new era of Tory sleaze.”
Mr Johnson defiantly stood by Mr Jenrick yesterday - repeatedly declaring the matter “closed”.
The Housing, Communities and Local Government Secretary is fighting to keep his job after documents revealed the extent of the contact between himself and Mr Desmond before the Cabinet minister signed off on the 1,500-home Westferry Printworks scheme in east London.
The pair exchanged text messages following a meeting at a Conservative Party event in November, and officials in Mr Jenrick's department described the minister as being "insistent" that the project be given the green light before a new levy added millions to the cost.
In texts to the Minister, Mr Desmond said the levy would add £45 million to the cost of the development, and said he didn’t want to give “marxists loads of doe (sic) for nothing.”
Mr Jenrick later had to quash his own approval, conceding that the decision was "unlawful" due to "apparent bias".
