The attorney general, Victoria Prentis, and her close family members have shares in six FTSE 100 companies worth more than £130,000 that have never been publicly disclosed, the Guardian can reveal. Prentis and her family members hold shares in BP, Tesco, HSBC, Lloyds, the beverages multinational Diageo and the defence contractor Rolls-Royce. The financial stakes have not been disclosed in parliamentary or ministerial registers, despite posing potential conflicts of interest. Their financial interests are being revealed today by a Guardian investigation into the effectively secret shareholdings of more than 50 members of parliament. All of the financial stakes of Prentis and her close family members are under the £70,000 threshold required for disclosure of shares under House of Commons transparency rules. However, some could arguably be subject to the requirement on MPs to register any interest that might reasonably be thought to influence their actions, speeches or votes. Prentis, who as attorney general has a wide-ranging and powerful brief that could affect any number of companies, personally holds shares in the defence contractor Rolls-Royce and previously held shares in BP and Tesco. The Tesco shares were held while she was in a previous ministerial job in the Department for Environment, Food and Rural Affairs (Defra), where she met lobbyists for the supermarket chain six times. The Tesco shareholding was not publicly disclosed in the list of ministers’ interests. While Prentis no longer holds shares in Tesco, other family members do. Two of her close relatives also hold stakes in Diageo, each worth more than £41,000. The close family members are not in her household, but their financial interests could be perceived as creating potential conflicts of interest for the minister. Prentis is also listed as a former shareholder in BP. It is not clear when she ceased owning a stake in the company or whether the shareholding overlapped with her time as a Defra minister. Her spokesperson declined to comment on any of her or her family’s shareholdings, which were identified in company shareholder registers. The registers, which are only accessible by members of the public in specific circumstances, were secured by the Guardian after formal legal requests. A barrister who worked as a government lawyer before being elected MP for Banbury in 2015, Prentis was appointed as attorney general by Rishi Sunak in October 2022. Her father, Tim Boswell, was an MP until 2010. The former attorney general Dominic Grieve told the Guardian the role’s functions required a “superabundance of caution” towards potential conflicts of interest. The attorney general has powers on judicial proceedings such as prosecutions and appeals on sentencing. Grieve said he had moved all of his and his wife’s investments into a blind trust upon his appointment as attorney general in 2010. This involves moving investments into a trust managed by an independent third party, removing the ability to affect individual investments. The trustees can be given general directions about the nature of the investments by the beneficiary, but they do not give specific information on the shares in the trust. But this did not completely resolve the potential for conflicts of interest, Grieve said. “There was still an issue – I knew what I had at the time I became a minister,” he said. “And if for any reason an issue might have arisen when I was attorney general that might have related to issues to shareholdings I knew I had, there might have been a conflict of interest, in which case I’d have flagged it up with my private office and the solicitor general would have dealt with the matter. That didn’t arise but that’s the sort of issue you need to think about.” Prentis’s most recent entry in the list of ministers’ interests is sparse. It states she is a trustee of a family trust but provides no further information on the holdings or beneficiaries of the trust. While she was a Defra minister, the list of ministers’ interests in May 2022 did note that Prentis held shares in the consumer goods group Reckitt Benckiser, raising a question about why other shareholdings were not declared.