A procession of former PMs could appear before a 'Line of Duty'-style Parliamentary inquiry into lobbying, it was revealed today.
A roll call of power players is expected to be summoned by the Public Administration and Constitutional Affairs Committee after it vowed to expose issues with the system.
David Cameron, who has faced a wave of criticism about his lobbying of ministers on behalf of Greensill, has already indicated he would give evidence.
Gordon Brown, Tony Blair and John Major are also considered likely to be called as the committee looks at the 'revolving door' between government and business.
Theresa May is the only living premier who might not be grilled, as she is still an MP serving in the Commons.
The PACAC probe is one of a bewildering array of inquiries being launched into ties between politics, Whitehall and business.
Mr Johnson has ordered a Cabinet Office investigation overseen by legal expert Nigel Boardman as he scrambles to defuse the lobbying row.
Mr 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. He has denied breaking rules, but admitted he should have used more formal routes to make approaches.
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.
In the latest revelations today:
David Cameron (left), who has faced a wave of criticism about his lobbying of ministers on behalf of Greensill, has already indicated he would give evidence. Tony Blair (right) could also be called
Theresa May is the only living former PM who might not be grilled, as she is still an MP serving in the Commons
Gordon Brown and John Major could be summoned by the Parliamentary Administration and Constitutional Affairs Committee to discuss the issues of links between government and business
Hunt for Labour 'moles' in government
A network of Labour Party 'spies' is operating at the heart of Whitehall, feeding secret information to Sir Keir Starmer's team to destabilise the Government, senior Tory sources claim.
The moles – Labour-sympathising civil servants – are believed to have played a key role in triggering the lobbying scandal which has allowed Sir Keir's party to construct a narrative of 'Tory sleaze' by leaking details of David Cameron's contacts with Ministers and officials.
They are also suspected of using leaks to try to 'sabotage' the Brexit withdrawal negotiations last year, and to provide advance notice to the Labour leader about Government policies in the pipeline – giving him time to structure his responses.
The Tory spy-hunters believe a 'cell' of Labour supporters, centred on the Cabinet Office, was activated last year after Dominic Cummings, Mr Johnson's former senior adviser in No 10, declared that a 'hard rain' was coming for the Civil Service as part of planned reforms to break up Whitehall's grip on the establishment.
Mr Cummings is a long-standing critic of the Whitehall establishment, describing the permanent Civil Service as 'an idea for the history books' and proposing the abolition of senior civil servants' roles.
Mr Wragg told the Sunday Telegraph: 'PACAC may not be the AC12 of Whitehall, nor do we envisage encountering anything quite as exciting as in a TV drama.
'However, it is at least a sense of duty that motivates our work, just as duty and service motivates the vast majority of those in public life.
'We must not let the questionable judgment of a few tarnish all.'
One source told the paper the committee 'will be keen to get the experience of other former PMs'.
Mr 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.
In interviews this morning, Environment Secretary George Eustice said the Government would be looking at whether changes were required - but insisted the current system for declaring interests was 'pretty good'.
He told Sky News' Ridge On Sunday: 'I think the right thing is for these reviews to go through their process, to conclude, to work out exactly what did and what did not happen and then yes, of course there may come a time after that when it is right to consider tweaks to policy.
'But fundamentally, I think the systems we have in place with ministers declaring interests with the ministerial code and the focus on that and how ministers conduct themselves in office is actually a pretty good one.
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
'But that is not to say you couldn't make tweaks or changes, and also there will be a time and a place for that after these reviews have concluded.'
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.
Commons standards chief calls for probe into suspicion David Cameron lobbied Philip Hammond to back investment fund set up by friend Lord Chadlington
An inquiry into lobbying by David Cameron should also examine a meeting that the former Prime Minister had with Philip Hammond amid suspicion that he may have used it to pressure the Government into supporting a lucrative £700million UK -China investment fund, according to the Chairman of the Commons Standards Committee.
As PM, Mr Cameron – the subject of an independent inquiry by lawyer Nigel Boardman over his lobbying of Ministers and Whitehall officials on behalf of loans firm Greensill Capital – hailed a 'golden era' in trade relations between Britain and China.
After leaving Downing Street, he seemingly hoped to cash in with a new private equity fund proposed by his friend Lord Chadlington, who had donated thousands of pounds to his Tory leadership campaign.
By January 2018, Mr Cameron was back in Beijing, this time for talks with Chinese President Xi Jinping (pictured together) about the initiative which could potentially net him millions
Mr Cameron flew to Beijing in September 2017 to discuss the plan with China's Vice Premier Ma Kai.
In October that year – 15 months after stepping down as PM – he met with Mr Hammond, the then Chancellor, and two months later the Treasury gave its crucial support for the fund for which Mr Cameron was to be Vice-Chairman.
By January 2018, Mr Cameron was back in Beijing, this time for talks with Chinese President Xi Jinping about the initiative which could potentially net him millions.
'Excellent meeting & enjoyable dinner with President Xi Jinping in Beijing, to talk about the 'Golden Era' in UK-China relations & plans for the new UK-China Fund,' he tweeted at the time.
Mr Cameron's office last night said his meeting with Mr Hammond had been only to seek Government support for the 'concept of a bilateral fund' and he had not lobbied Ministers on behalf of the fund's investors or partners.
He informed the Advisory Committee on Business Appointments (Acoba), which advises former Ministers and civil servants on outside employment, about the meeting, his representatives added.