In a letter to the prime minister – released alongside an apology from Mr Johnson – Lord Geidt describes the omission as ‘extraordinary”.
“I consider that the greatest possible care should have been taken to assemble all relevant material and this standard has not been met,” the letter states.
It adds: “As a result, I believe this episode demonstrated insufficient regard or respect for the role of independent adviser.”
Mr Johnson’s attempts to “reclaim public confidence” over the flats controversy – which broke electoral law, the Electoral Commission found – have been damaged.
The prime minister has blamed a new mobile phone number for the lapse – and still faces the threat of a further inquiry by the parliamentary commissioner for standards.
Interviewed at a vaccination centre, he was asked if he expected people to believe he had forgotten to disclose key evidence simply because it was no longer stored on his phone.
“I followed the ministerial guidance at all times – and yes,” he replied, declining to expand on what happened.
Messages between Mr Johnson and Lord Brownlow reveal him describing the historic flat above 11 Downing Street – where he lives with his wife Carrie – as “a tip”.
“I am afraid that parts of our flat are still a bit of a tip and am keen to allow Lulu Lytle to get on with it,” he wrote, of the designer whose wallpaper sells at more than £800 a roll.
Labour alleged that the exchange of letters revealed a prime minister with “little regard for the rules or the truth”.
“It is simply impossible to read these exchanges and conclude that the prime minister has not breached these aspects of the code.
“Once again, by attempting to hide the truth, Boris Johnson undermines his own office. The prime minister’s pathetic excuses will fool no one, and this is just the latest in a long line of sorry episodes.”
The controversy over the £142,000 refit, £30,000 funded by the taxpayer, was reignited when an Electoral Commission report revealed Mr Johnson personally asked for more funds for the redecorations, in 2020.
Yet – three months later – he told Lord Geidt that he nothing about the way the work was being funded, leading to the adviser’s inquiry clearing him.
In his letter to his watchdog, sent on 21 December, the prime minister offered a “humble and sincere apology” for a mix-up he blamed on replacing his phone number due to “security issues”.
Therefore, he “did not have access to my previous device and did not recall the message exchange”.
Lord Geidt’s reply stated that he still does not believe there had been a breach of the ministerial code, but does not appear to deliver Mr Johnson a full exoneration.
He expresses “doubt” whether he would have concluded, in his original report, that the prime minister “took steps to make the relevant declaration and to seek advice”.
“This new information and its omission from the original exercise has caused me to test my confidence in my earlier conclusions,” the adviser writes.
The Cabinet Office’s failure to seek information from Lord Brownlow had “the effect of excluding the missing exchange from the documentary record that was provided to me”, he states.
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