Tax officials are understood to be examining whether David Cameron failed to fully disclose taxable perks such as flights on private planes when he worked for the collapsed lender Greensill Capital, the Guardian can reveal.

In particular, officials are said to be looking at a number of flights that took off or landed near his house in Oxfordshire and also in Cornwall, where the foreign secretary has a holiday home. They are also examining an offshore trust that it is understood was created by Greensill to pay him extra benefits.

It comes amid wider concerns that the process for appointing the former prime minister to the House of Lords, and other background checks for his cabinet appointment, were rushed through in a bid to keep the details of Rishi Sunak’s reshuffle secret.

Cameron was embroiled in the Greensill lobbying scandal after he exploited contacts gathered during his tenure as prime minister to try to win business for the now defunct supply-chain finance company at the start of the pandemic in early 2020.

A parliamentary inquiry later found that he exercised “significant lack of judgment” in lobbying for Greensill, in which he held a “very significant personal economic interest”, by sending dozens of text messages to officials and ministers including Sunak, the then chancellor.

He has also worked extensively in the UAE and for organisations linked to the Chinese government since leaving office.

Cameron was appointed as foreign secretary last Monday. Two senior officials told the Guardian they believed he would probably fail the security checks required for a senior civil servant in the Foreign Office because of his multiple meetings with Chinese politicians and business figures since resigning as prime minister.

Officials are looking at whether Cameron declared all the so-called benefits in kind during his work for Greensill between 2018 and 2021. These are taxable services given to staff by an employer on top of their salary, and can be free or at a very low cost. A spokesperson for Cameron told the Guardian that he has paid all his taxes in full.

Flight logs seen by the Guardian show at least 13 flights to and from Newquay airport in Cornwall, which are understood to have been for the benefit of the former prime minister, on Greensill’s Piaggio P180 private aircraft. Flight logs also show two involving RAF Brize Norton, again understood to have been for the benefit of Cameron. Brize Norton is a short drive from his Oxfordshire home.

Cameron has holidayed extensively in Cornwall for many years, favouring the coastal resort of Polzeath as a destination while prime minister. In 2017, it was reported that he paid £2m for a holiday home nearby.

It is unclear what the flights were worth. A report in the Australian Financial Review said Greensill leased a Piaggio aircraft to another division for an hourly rate of £1,600, while the Financial Conduct Authority said in a 2022 report that a single flight to Sardinia on a Greensill private plane, taken by a disgraced fund manager, was worth £15,000.

The evidence of flights is not believed to be exhaustive, with sources claiming that there were several more flights gifted to the foreign secretary by his then employer. Such flights would constitute a benefit in kind, but the employer’s national insurance contributions and Cameron’s personal tax liabilities may not have been paid, sources believe. He may therefore face an outstanding tax bill on each of these flights.

A spokesperson for Cameron said: “As already made clear in David Cameron’s evidence to the Treasury select committee in May 2021, he did use Greensill’s company plane a number of times on a personal basis, all for short-haul flights, and tax was paid appropriately for any benefit received. Further, all income received from Greensill has been properly declared to HMRC and all tax paid in full.”

A spokesperson for HMRC said: “We cannot comment on identifiable taxpayers.”

There may also be further income tax liabilities to address, sources said. Cameron was paid for his work at Greensill via an employee benefit trust in Guernsey, a tax haven in the Channel Islands. It appears that Lex Greensill, the company’s founder, paid shares into and created this trust as a way to effectively pay Cameron an additional benefit. UK income tax, rather than a lower rate of capital gains tax, may therefore have been payable on the £7m in salary and shares that Cameron is said to have received via the trust, according to sources who valued it at £20m prior to the company’s collapse.

Founded by Greensill, an Australian banker from farming stock, his company drew controversy for its links to the steel and commodities trader Sanjeev Gupta, providing huge sums to his steel and energy empire and related companies. This included £400m of Covid loans, backed by taxpayer guarantees. The Gupta Family Group Alliance, a loose collection of companies headed by Gupta, has been under investigation by the Serious Fraud Office since 2021.

Greensill now faces a criminal case in Switzerland along with former bankers at Credit Suisse. The case is linked to the collapse in funds worth about £7bn which were mostly invested in his eponymous firm.

A spokesperson for Lex Greensill declined to comment on his activities at Greensill Capital. A lawyer for Greensill has previously declined to comment on the ongoing Swiss case.