LONDON (REUTERS) - British Prime Minister Boris Johnson "unwisely" allowed a refurbishment of his flat to proceed without more rigorous consideration of how it would be funded, the independent adviser on ministers' interests said in a report.

Mr Johnson has in recent weeks faced intense scrutiny over how the refurbishment of his flat, estimated in some media reports to have run into hundreds of thousands of pounds, had been financed.

On Friday (May 28), an adviser on ministerial behaviour, Mr Christopher Geidt, published a report into the issue, which cleared the Prime Minister of a conflict of interest, or of breaching the ministerial code.

But the report was nevertheless critical of Mr Johnson.

"The Prime Minister - unwisely, in my view - allowed the refurbishment of the apartment at No 11 Downing Street to proceed without more rigorous regard for how this would be funded," the report said.

The report found that a Conservative Party donor had settled an invoice for some of the refurbishment cost, but said Mr Johnson was unaware of this and later settled the invoice himself.

Mr Geidt said no conflict of interest had arisen.

"I have considered the nature of that support and am content that no conflict (or reasonably perceived conflict) arises as a result of these interests," the report said.

"Having advised that the interests declared by the Prime Minister present no actual or perceived conflict, I consider them to be consistent with the provisions of the Ministerial Code."

Separately, Britain's Electoral Commission has launched an investigation into the funding of work on the Prime Minister's apartment, saying there were grounds to suspect an offence had been committed.