The comment comes despite an expert warning that politicians must quickly declare any gifts or loans that “benefits them in connection with any political activities”.
“The person who has to report is the donee, the money to whom the money is given or loaned,” Professor David Howarth, a former Electoral Commissioner, said this week.
But – after Mr Johnson was accused of being “mired in sleaze, cronyism and scandal” at a stormy prime minister’s questions – his press secretary played down the possible consequences for him.
The party would “provide all necessary information to assist the Commission,” she said, repeating that it was “a matter for the Conservative Party as a political party”.
However, the press secretary – asked if that meant Mr Johnson was “in the clear” – acknowledged: “I’m not sure that there’s anything on that yet.”
And asked whether the Commission had contacted the prime minister to say he is not under investigation, she replied: “I don’t think I’ve seen any correspondence yet.”
The ‘sleaze’ crisis engulfing the prime minister deepened when the Commission announced: “We are now satisfied 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.”
The announcement came after days of Mr Johnson, and other ministers, failing to deny that the Conservative Party, or a Tory donor, originally funded the lavish redecoration.
It is believed the party secretly approved paying a £58,000 bill as long as nine months ago – a payment then covered by a wealthy donor, according to a leaked email.
The watchdog has the power to issue a “disclosure notice” about its investigations, which could require the prime minister and the party to release documents.
If it fails to get the information it is seeking, an “inspection warrant” can be used to search premises – and individuals may also be required to attend interviews.
The investigation will be into any offences committed under the Political Parties at Elections and Referendums Act, passed in 2000, which sets out the law surrounding donations.
The Commission can issue fines of up to £20,000, but it can also refer investigations to the police or prosecutors.
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