(CNN) Diplomatic cables sent from the United Kingdom's ambassador to the United States back to London describe President Donald Trump as "inept," "insecure" and "incompetent," a UK government official confirmed Saturday to CNN.

The leak could cause serious diplomatic damage between the two " special relationship " allies.

While foreign envoys of all nations are often candid in classified dispatches back home, there are periodic episodes when such assessments leak, causing great political embarrassment. Months of efforts by the ambassador, Kim Darroch and his diplomats to build ties and trust with Trump and his political acolytes will be undermined.

On Monday, Trump said that the White House would no longer "deal with" Darroch.

The cables were leaked to and first published by the Daily Mail

Darroch used secret cables and briefing notes to warn the UK government that Trump's "career could end in disgrace," and described conflicts within the White House as "knife fights," according to the Daily Mail.

A UK government source told CNN the memos described in the Daily Mail story are genuine.

The Daily Mail says the memos span the period between 2017 to present day, covering everything from Trump's foreign policy to his 2020 reelection plans.

In one memo dated June 22, according to the Daily Mail, Darroch questioned Trump's claim that he pulled back from retaliating against Iran last month after the downing of a US drone because the President was told at the last minute that US air strikes could kill 150 Iranians.

He also said in a cable to the Foreign Commonwealth Office that while he believed Trump can't afford to lose much support, he thinks there's still a "credible path" for his reelection.

The White House told CNN it had no comment on the story.

The leaked cables come at a sensitive time in UK politics with Conservative Party members currently electing a new prime minister to succeed Theresa May, who was effectively toppled by her own members of Parliament for failing to deliver on her country's 2016 vote to leave the European Union.

"The British public would expect our Ambassadors to provide Ministers with an honest, unvarnished assessment of the politics in their country. Their views are not necessarily the views of Ministers or indeed the government. But we pay them to be candid. Just as the US Ambassador here will send back his reading of Westminster politics and personalities," a statement from the British FCO said.

"Of course we would expect such advice to be handled by Ministers and civil servants in the right way and it's important that our Ambassadors can offer their advice and for it remain confidential. Our team in Washington have strong relations with the White House and no doubt that these will withstand such mischievous behaviour," the statement continued.

The favorite for the job, Boris Johnson, is seen as likely to seek to forge a much closer relationship to Trump than May, who made strenuous efforts to court the President and developed a respectful relationship but never really bonded with him politically. If it leaves the EU, Britain will be seeking to seal a bilateral trade deal with the US and Trump is expected to drive a hard bargain. So there will be speculation that the leak of Darroch's memos was a politically motivated act by someone in London to clear space in Washington for an outspokenly pro-Brexit ambassador.

Darroch also used to work as national security adviser to former British Prime Minister David Cameron and as a top UK representative to the EU, so although he's a career diplomat, he is not seen as philosophically aligned with the crowd of hardcore Brexiteers expected to take over 10 Downing Street.

Johnson is unpredictable, politically incorrect, a populist and deeply critical of the EU and is often accused of blurring facts -- traits which he shares with Trump.

There is so far no reaction from the President's Twitter feed.

But Trump has never felt constrained from criticizing the British government.

Several times, he has embarrassed May after criticizing her handling of Brexit negotiations. He plunged into Britain's internal affairs in June by openly rooting for various Conservative candidates in the leadership elections. And he has waged a long-running feud with London's mayor Sadiq Khan.

Trump also raised some eyebrows in the UK by repeatedly praising Nigel Farage, one of the most prominent campaigners for Brexit.

Farage rushed to Trump's defense on Sunday, tweeting : "Kim Darroch is totally unsuitable for the job and the sooner he is gone the better."

Darroch had been riding high on the success of Trump's trip to the UK in June which largely went off without a hitch. His position with the Trump administration however now looks difficult at best. Though his memos are deeply sensitive given the source, the unflattering depiction of the Trump White House is one that will be recognizable to readers of US media outlets.

This story has been updated with additional developments and context.