It comes after it was announced that Lord Geidt will be the new “independent adviser” on ministerial standards.
The crossbench peer, who was the Queen’s private secretary for 10 years, will lead a probe into the funding of the makeover. He is also expected to advise the PM on any further registration of interests that may be needed.
The PM’s official spokesman said Mr Johnson had concerns that an independent adviser with powers to launch probes could be drawn into an investigation with "trivial or vexatious complaints". He added: “So he will remain the ultimate arbiter of this.”
Asked if that meant the PM could reject any findings on himself, the spokesman said: "The Prime Minister will remain the ultimate arbiter of this, yep.”
Lord Geidt’s new post has been vacant since Sir Alex Allan resigned in the wake of the Priti Patel bullying scandal.
Sir Alex quit after Mr Johnson overruled him on an investigation into Ms Patel’s behaviour.
The ministerial code sets out the standards of conduct expected of ministers and how they discharge their duties.
When it comes to Mr Johnson’s flat renovations, the Government has so far refused to say whether he received a loan from the Tory Party to pay for the renovations that were above the annual allowance.
If this is the case, the PM would be expected to show that it was consistent with the code which makes clear there should be "no actual or perceived conflicts of interest".
A parallel inquiry is being conducted by Cabinet Secretary Simon Case. Meanwhile the Electoral Commission announced this morning it was launching its own investigation saying there was "reasonable grounds" to suspect an offence may have occurred.
Mr Johnson told Prime Minister’s Questions he “personally” paid for the renovations, but refused to answer whether he received an initial loan from the Tory party.