Cabinet secretary and head of the civil service Simon Case and the head of the Cabinet Office propriety and ethics team Darren Tierney will face questions from the cross-party House of Commons Public Administration and Constitutional Affairs Committee.
The hearing will kick off the committee’s inquiry into the effectiveness of codes of conduct for ministers and officials in the light of the scandal over former prime minister David Cameron’s lobbying for failed finance company Greensill.
The development came as Labour demanded the release of records of all texts, calls and meetings with lobbyists by chancellor Rishi Sunak to discuss changes to tax rules and Covid-19 support scheme.
On Wednesday, Mr Johnson agreed to publish his private communications on Covid contracts - though it was unclear whether the promise related only to exchanges with vacuum cleaner tycoon James Dyson or covered contacts with other business figures and lobbyists.
Shadow chancellor Anneliese Dodds wrote to Mr Sunak to urge him to follow the PM’s lead in order to “restore public trust that your decisions and those of HM Treasury were taken exclusively in the public interest”.
Heavily-redacted documents released by the Treasury last night revealed the extent of lobbying - described as “persistent” by the department’s top mandarin - by Mr Cameron and company founder Lex Greensill as the Covid crisis hit in the spring of 2020.
The emails and letters showed that the Treasury was made aware as early as March 2020 that the company was in “serious and urgent funding difficulties”, with Mr Greensill warning that “timely support” was needed from the government’s Covid support scheme.
And minutes of a phone call on 30 March showed that he told Treasury officials he had “grave concern” that many tens of thousands of small businesses would miss out on payments the following week if Greensill was not helped.
But an internal memo revealed Treasury scepticism about Greensill, with one unnamed official noting that the businessman was unwilling to list his major investors in full or confirm that all his suppliers were from the UK.
Ms Dodds said the cache of messages proved that the Treasury was aware of Greensill’s financial difficulties three months before the company was granted access to hundreds of millions of pounds of taxpayer-backed loans through accreditation to the Coronavirus Large Business Interruption Loan Scheme (CLBILS).
And she said it confirmed that Greensill discussed its application to the scheme with Treasury officials on 24 April, the day after Mr Sunak texted Cameron to say he had “pushed” his team to explore options with the Bank of England.
“Rishi Sunak has been running scared of his role in the sleaze that is engulfing the Conservative Party, but the longer he hides from scrutiny the more questions it raises,” said the shadow chancellor.
“We now know that his officials were fully aware that Greensill Capital was in financial trouble months before the government opened the door for it to lend hundreds of millions of pounds of taxpayer-backed loans.
“But we don’t know what the chancellor told David Cameron he ‘pushed his team’ to do a day before Greensill’s affiliation to a Covid loan scheme was discussed at the Treasury, or what role he played in dishing out tax breaks by text to Sir James Dyson.
“The chancellor should come clean by publishing in full the details of every text, every message and every secret meeting he had with lobbyists about changes to tax rules and Covid-19 support schemes.”
Mr Case, who took over as the prime minister’s top civil servant in September, is certain to be asked on Monday about what one senior parliamentarian yesterday warned were “the dangers of government by WhatsApp”.
He is likely to be pressed to confirm or deny reports that he personally advised Mr Johnson to change the mobile phone number he has held for more than a decade, due to concerns over the volume of direct contacts he was receiving from people outside government.
Mr Tierney will face challenges over whether the ministerial code of conduct remains fit for purpose and whether Mr Johnson should remain the final judge of whether ministers found to have breached it should lose their jobs.
Controversially, the government has confirmed that the PM alone will decide on any action resulting from a separate internal inquiry into the Greensill affair being carried out by lawyer Nigel Boardman.
And both will face questions over why no independent adviser on ministerial interests has been appointed, five months after the resignation of Sir Alex Allan over Mr Johnson’s refusal to accept his finding that Priti Patel had bullied Home Office staff.
The PACAC inquiry is one of seven launched into the Greensill affair since it first emerged that Mr Cameron, who was employed as a senior adviser by the firm, had contacted Mr Sunak by text message to appeal for help.
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