Nadhim Zahawi failed to tell officials that he had exchanged WhatsApp messages with David Cameron when the former PM was contacting ministers about Greensill Capital loans, it has been reported.

The Tory chair – fighting for his political life after admitting he had to settle a tax dispute with HMRC – wrongly told investigators that he had not exchanged messages with Mr Cameron, according to The Times.

A probe by the Information Commissioner’s Office (ICO) found that Mr Zahawi did not tell officials about messages from Mr Cameron looking for help with contact details, the newspaper said.

Mr Zahawi later admitted messages were exchange – but said they had been deleted, after their existence was established and the ICO returned to ask him again about the communication.

Mr Cameron’s work lobbying for loans for the failed finance firm Greensill sparked a scandal in 2021, when the former PM admitted he should have communicated with ministers through “formal channels” rather than text and WhatsApp.

The former Tory leader wrote to Mr Zahawi that founder Lex Greensill “says you are being v helpful over HMT and CBILS programme. Would it help if I pinged a message to Richard Sharp? I used to see him a bit in early leadership days but haven’t so much recently […] All good wishes Dc.”

The ICO inquiry stated: “It is our understanding that Mr Zahawi does not know how the WhatsApp messages from Mr Cameron came to be deleted from his mobile phone.”

It comes as Mr Zahawi comes under growing pressure to set out the details of his estimated £5m tax settlement with HMRC, with some Tory MPs telling The Independent his position was “untenable”.

Labour has called for Mr Zahawi to publish his tax returns for the past five years, and demanded that Rishi Sunak “come clean on what he knew and when” about his minister’s tax affairs.

The Tory chair had previously claimed that inquiries by HMRC into his taxes – first revealed by The Independent – were a “smear”. But he admitted on Saturday that “questions were being raised about my tax affairs” when he was being appointed chancellor by Mr Johnson in July.

A government source told Sky News Mr Zahawi settled his tax problem with HMRC while he chancellor, but his representatives have yet to confirm the precise timing of the settlement.

Mr Zahawi has not yet confirmed that he paid a fine to resolve his “careless” error. But his spokesman has not denied he paid a penalty. He reportedly paid an estimated £4.8m – including a 30 per cent penalty of around £1m.

As Labour tried to put pressure on Mr Sunak, No 10 is thought to be ready to argue that the PM only knew that Mr Zahawi paid a penalty to HMRC as part of his settlement when details emerged on Friday.

But it has also been reported that the Tory chair was rejected for a knighthood over concerns about his tax affairs. Whitehall officials blocked the honour after checking with HMRC about Mr Zahawi’s tax affairs in December, according to the Sun on Sunday.

Sir Edward Troup, former permanent secretary at HMRC, said the body had a traffic-light system – red, amber and green – to warn the government of the potential risk in giving a knighthood to those who have had tax problems.

The Cabinet Office’s propriety and ethics team raised issues around Mr Zahawi’s tax affairs directly with Boris Johnson before he made him chancellor, according to ITV News.

Labour’s shadow culture secretary Lucy Powell told BBC Radio 4’s Today programme: “His position is totally untenable, and it shouldn’t be a case that we are sitting around waiting for him to resign – the prime minister should be sacking him.”