Boris Johnson will face formal investigation into apartment renovation costs

(CNN) — Britain’s political spending watchdog will launch a formal investigation into the funding of renovations to Prime Minister Boris Johnson’s apartment in Downing Street.

The UK’s Electoral Commission said in a statement Wednesday that there “are reasonable grounds to suspect that an offence or offences may have occurred. We will therefore continue this work as a formal investigation to establish whether this is the case.”

Johnson has been under pressure to explain how he paid for the renovations to the apartment, which British news outlets have reported cost around £200,000 ($280,000).

The Prime Minister has faced further scrutiny after his former chief aide last week leveled accusations of unethical behavior.

Dominic Cummings, who left his role as Johnson’s former chief adviser late last year after gaining a reputation as the driving force behind the Prime Minister’s Brexit policy and re-election, alleged in a blog post that Johnson planned to have Conservative Party donors pay for the upgrade.

A Number 10 spokesperson told CNN that the government has “transparently laid out the historic expenditure” and that “any costs of wider refurbishment … have been met by the Prime Minister personally.”

The commission added in its Wednesday statement that “the investigation will determine whether any transactions relating to the works at 11 Downing Street fall within the regime regulated by the Commission and whether such funding was reported as required.”

CNN has reached out to the PM’s office for comment