BORIS JOHNSON should “just come clean” with the British people over his villa Mustique holiday, Labour demanded at the weekend.

The Prime Minister’s holiday to the private Caribbean island 16 months ago could have cost more than double the £15,000 he declared in the Commons register, the parliamentary standards watchdog found on Friday.

Commissioner for Standards Kathryn Stone said the bill for the luxury break had not been met by Tory donor David Ross as Mr Johnson has insisted.

She said she was still investigating whether the PM properly declared the trip with his fiancee Carrie Symonds. Her verdict was delivered to Mr Johnson months ago.

The PM told Ms Stone that the pair got the villa for half price as a last-minute bargain, according to the Daily Mail.

He argued that, although the villa they stayed at was not owned by Mr Ross, the Carphone Warehouse co-founder effectively paid for it because it was part of a time-share.

Mr Johnson said it was a “benefit in kind” from the tycoon and admitted that while the deal was “unconventional,” there was nothing “improper” about it.

Mustique is part of St Vincent and the Grenadines, a tax haven where offshore trusts, used to avoid tax, are common.

The PM is already facing investigations into whether he properly declared any donations to cover the lavish refurbishment of his Downing Street flat.

Labour deputy leader Angela Rayner said: “The public have a right to know who paid for his luxury holiday, how much they paid for it and what they might expect in return for their generosity. 

“If these reports are true, the Prime Minister will once again have shown his complete contempt for the basic standards of integrity in office.

“The Prime Minister has already broken parliamentary rules regarding his financial interests. It is clear that he thinks that the rules that apply to the rest of us simply do not apply to him.”

Mr Johnson was said to have refused to accept the commissioner’s ruling and is trying to have it overturned to avoid the risk of being suspended as an MP.

Downing Street has insisted the Prime Minister “transparently declared the benefit in kind” of the luxury Caribbean holiday and noted that Mr Ross confirmed the declaration was “correct.”