The police watchdog has said an announcement on whether to investigate Boris Johnson’s involvement with the American tech entrepreneur Jennifer Arcuri could still be published before the election.

The Independent Office for Police Conduct (IOPC) strongly denied reports that it had delayed its announcement over whether the prime minister could face an investigation into “possible criminality” until after the Christmas poll.

As mayor of London, Mr Johnson was responsible for policing, prompting the IOPC to become involved in investigating whether there was a conflict of interest over Ms Arcuri’s treatment due to the pair’s friendship.

Ms Arcuri, a former model, received a £100,000 grant for her company Hacker House last year, and also accompanied Mr Johnson on several trade missions while he was in City Hall.

Opposition politicians reacted with fury to a report in The Observer which cited sources in the IOPC, who said it had been about to announce whether it was proceeding with a criminal investigation but decided to delay until after the election.

Top 10 marginal seats to watch at the general election Show all 10 1 /10 Top 10 marginal seats to watch at the general election Top 10 marginal seats to watch at the general election North East Fife Currently held by the SNP with a majority of 2 Getty Top 10 marginal seats to watch at the general election Kensington Currently held by Labour with a majority of 20 Getty Top 10 marginal seats to watch at the general election Perth and North Perthshire Currently held by the SNP with a majority of 21 Getty Top 10 marginal seats to watch at the general election Dudley North Currently held by independent, formerly Labour, MP Ian Austin with a majority of 22 LivingInMediocrity Top 10 marginal seats to watch at the general election Newcastle-under-Lyme Currently held by Labour with a majority of 30 Derek Harper Top 10 marginal seats to watch at the general election Southampton Itchen Currently held by the Conservatives with a majority of 31 Rob Candish Top 10 marginal seats to watch at the general election Richmond Park Currently held by the Conservatives with a majority of 45 Robin Webster Top 10 marginal seats to watch at the general election Crewe and Nantwich Currently held by Labour with a majority of 48 Jaggery Top 10 marginal seats to watch at the general election Glasgow South West Currently held by the SNP with a majority of 60 Alec MacKinnon Top 10 marginal seats to watch at the general election Glasgow East Currently held by the SNP with a majority of 75 Christine Johnstone

However the IOPC told The Independent that it was still possible that the decision could be made before the 12 December poll – but suggested it was unlikely to report in time.

In a statement, the watchdog said: “The IOPC strongly refutes claims published in The Observer. This matter has not been finalised.

“We have not delayed any announcements on the status of this referral.

“Our assessment of this matter is ongoing as we continue to collect information and seek legal advice.”

The news will come as a blow to the prime minister as he seeks to get on the front foot after a challenging start to the election campaign marred by the resignation of a cabinet minister.

But the row over his friendship with Ms Arcuri is unlikely to fade. The London Assembly also launched a probe into the row but it has now paused its efforts at the request of the IOPC.

A third inquiry, commissioned by London mayor Sadiq Khan, has also been scaled back temporarily at the watchdog’s request.

Labour’s Jon Trickett, the shadow minister for the cabinet office, condemned any delay to the publication of the findings.

He said: “This is an unacceptable decision and should be reversed immediately.”

Caroline Pidgeon, a Lib Dem member of the London assembly’s oversight committee, said: “It raises questions over how independent the IOPC really is and whether the prime minister’s lawyers have been exerting undue pressure.”