The parliament's standards watchdog opened a probe into Sunak on April 13 under paragraph 6 of the code of conduct over suspicion of a conflict of interests with the stake owned by his wife, Akshata Murty, in Koru Kids, a childcare firm that bills itself as a start-up run by an entrepreneur-mother from London.
Last month, Sunak's cabinet announced a pilot scheme for public funding of private daycare facilities in a bid to grow the childminding market. The probe was launched to determine whether Sunak's wife could benefit from government funding.
The probe was later expanded on April 20 to add paragraph 13 of the code, saying that members of parliament should not disclose details on an ongoing investigation, according to an entry on the parliament's website.
Sunak, a former investment banker, is known as one of the wealthiest UK prime ministers in history. He is married to the daughter of Indian billionaire Narayana Murthy.
Sunak's wife has reportedly not renounced her Indian citizenship and, thus, was able to avoid paying taxes on her business income received in other countries as a non-resident of the UK. Reports suggest that Murty was able to avoid paying £11.5 million ($14.3 million) in taxes on annual dividends by paying only £30,000 to retain her non-resident status in the UK.