Ahead of Prime Minister’s Questions, the Opposition party put a series of demands for Mr Johnson to answer.
Shadow Foreign Secretary Lisa Nandy told ITV’s Good Morning Britain: “We have got to get to the bottom of what has happened with this flat.
“Who gave the money?“ Why was it not declared?
“And who does the Prime Minister owe favours to?”
She stressed that Labour had “dragged ministers reluctantly” to Parliament to answer questions over the rows swirling around the Prime Minister.
“We will not rest until the public has answers,” she added.
Her comments came as it was reported that Mr Johnson reportedly told aides he could not afford the refurbishment of the flat as the costs started to spiral.
The Daily Mail alleged the Prime Minister told colleagues the bill was escalating out of control, while his chief of staff Dan Rosenfield was said to have felt the refurbishment was a “crazy arrangement” and a “mess”.
The newspaper said when aides asked the Prime Minister how much the upgrades were costing, Mr Johnson replied: “Tens and tens of thousands – I can’t afford it.”
The former de facto chief of staff, who left No10 last autumn after losing a power struggle, claimed in an incendiary blog last week that Mr Johnson had at least at one stage wanted donors to “secretly pay” for the work in an “unethical, foolish, possibly illegal” move.
A Tory donor is believed to have made a donation of £58,000 and that this money was initially used to pay for the refurbishment which was reportedly carried out by trendy designer Lulu Lytle.
A No 10 spokeswoman said renovation costs of Mr Johnson’s living quarters, beyond those provided for by the £30,000 annual allowance, had been “met by the Prime Minister personally”, adding: “Conservative Party funds are not being used for this.”
But Downing Street declined to deny suggestions that the Prime Minister received a loan from the Conservative Party to cover the initial costs, before repaying the party.
Cabinet Secretary Simon Case, head of the Civil Service, has been tasked with reviewing the refurbishment of the flat in No 11, while the Electoral Commission is also looking into the affair.