Boris Johnson's declarations for the Downing Street flat refurb will be published at the end of the month

An official review into the controversial refurbishment of Boris Johnson’s Downing Street flat will be published by the end of this month, according to the prime minister’s new standards adviser.

Lord Geidt, who was appointed to the independent role last month, said a long overdue register of all ministerial interests would also be released by the end of May.

"Public confidence, I think in my judgment, demands that this list be published without further delay," he told MPs on the Public Administration and Constitutional Affairs Committee.

The crossbench peer was asked to investigate the facts around the flat renovation following newspaper reports that money from a Conservative Party donor was initially used to pay for the work.

Boris Johnson receives an annual public grant of £30,000 to spend on upkeep and maintains he personally paid for any additional costs.

Lord Geidt said all ministers had been asked to resubmit private interests and described the five-month delay in publishing the new register as "unfortunate".

The former royal private secretary was appointed to the post following the resignation of Sir Alex Allan in November.

Sir Alex quit after Boris Johnson disagreed with his advice that Home Secretary Priti Patel had broken the ministerial code.

Asked if he would resign his position if the prime minister went against his advice, Lord Geidt said he hoped it "wouldn't come to that" but added "the power is there as a last resort".

The newly appointed adviser also confirmed that he had received assurances that he will have new powers to propose investigations and publish his advice on possible breaches of the ministerial code "in a timely manner".

However Tim Durrant, associate director at the Institute for Government, suggested his new powers may be weaker, tweeting that the terms of reference state that ministers retain the publishing powers.

Labour committee member Lloyd Russell-Moyle also criticised the fact that requests made to the prime minister to start an investigation will remain private.

"Those are all behind doors, there is no public scrutiny, there is no sunlight, disinfectant… none of that will happen at those early stages", said the Brighton MP.