Boris Johnson was today warned failure to tackle the 'shameful' lobbying storm could cost him votes as a crucial round of elections loom.
Senior Tory Sir Bernard Jenkin appealed for the PM to get a grip after a slew of revelations in the wake of Greensill Capital's collapse into administration.
Unless he is more 'transparent' the row could hit the 'Red Wall' support that delivered Mr Johnson's historic 2019 majority, Sir Bernard said.
The scale of damage could become clear within weeks, with a wave of elections on May 6 including councils, mayors and a by-election in Hartlepool - a seat traditionally held by Labour but within the grasp of the Conservatives if their working-class surge continues.
Senior Tory Sir Bernard Jenkin (right) appealed for Boris Johnson (left) to get a grip after a slew of revelations in the wakes of Greensill Capital's collapse into administration
Mr Johnson has ordered a Cabinet Office probe overseen by a legal expert as he scrambles to defuse the lobbying row.
David Cameron has been hit with criticism over securing access to ministers for finance firm Greensill, whose collapse now risks thousands of jobs, particularly in the steel sector.
The saga deepened last week after it emerged the former head of government procurement, Bill Crothers, took a part-time position with the firm while in his Whitehall post.
Writing in The Observer, Sir Bernard said the 'lines between public service and private gain' had become 'blurred'.
The MP, chair of the powerful Commons Liaison Committee, described the current situation as 'shameful' and 'utterly corrosive of public trust in government'.
'This should matter to Boris Johnson,' Sir Bernard said.
'He does not need to pretend to be a saint, but his ''red wall'' voters, who gave him his majority, will start to dismiss him unless he can show he is more open, more transparent and very different from the out-of-touch elite he defeated in the 2016 referendum and ousted from government.'
Labour is determined to keep the lobbying issue alive, believing the issue of Tory sleaze in Westminster is cutting through to voters.
The controversy over the relationship between Government and the private sector follows disclosures that Mr Cameron personally lobbied Chancellor Rishi Sunak on Greensill's behalf and was able to arrange for its founder, Lex Greensill, to have a 'private drink' with Health Secretary Matt Hancock.
Shadow chancellor Anneliese Dodds has written to Mr Sunak setting out 21 questions she wants answers to over his dealings with the former Tory leader and Greensill.
The questions include asking for more information about the 'proposals' mentioned by Mr Sunak in a text to Mr Cameron and why a further meeting between Greensill and Treasury officials took place on May 14 2020 'at the Chancellor's request'.
David Cameron has been hit with criticism over securing access to ministers for finance firm Greensill
In her letter, Ms Dodds told Mr Sunak that she was 'concerned' his dealings with the former No 10 incumbent 'may have constituted a breach of the ministerial code'.
'The Chancellor is running scared of scrutiny over his role in the Greensill affair, but the public demand answers,' said Ms Dodds.
The Sunday Times reported that Mr Cameron was able to assist the specialist bank in securing a lucrative NHS contract after he contacted a civil servant who had served under him in the Cabinet Office.
Mr Cameron reportedly emailed Matthew Gould, who had since moved on to head NHSX, the health service's digital arm last year about rolling out Greensill's advance payment app, Earnd, for doctors and nurses across the NHS.
The former Tory party leader has insisted he did not break any rules through his dealings but acknowledged there are 'lessons to be learned' and he should only make approaches to ministers through the 'most formal channels'.