Boris Johnson is being investigated by the parliamentary commissioner for standards over a holiday to the Caribbean in 2019
The investigation will look into who exactly funded his £15,000 villa during a holiday to Mustique.
Katharine Stone, the independent commissioner for parliamentary standards, will lead the investigation.
The investigation's official title "registration of interest under category 4 of the guide to the rules [Visits outside the UK] in 2020" under paragraph 14 of the code of conduct.
This comes alongside the Electoral Commission also looking into the circumstances around the prime minister's flat refurbishment, which some estimate could be as much as £200,000.
Johnson will become the first prime minister in history to be investigated by the commissioner for parliamentary standards.
The powers of the independent commissioner are wide-ranging, including having the power to suspend MPs and trigger by-elections, which is likely to cause serious concern at Number 10.
Johnson is not alone in being investigated, either - other Conservative MPs include earmarked by the commissioner include Owen Peterson, Theresa Villers, Jonathan Gullis, Natalie Elphicke, Bob Stewart, Adam Holloway, and Roger Gale.
