The official co-author and unofficial ghostwriter of Donald Trump’s 1987 memoir and business book, ‘The Art of the Deal’, has heavily criticised the Republican nominee’s ability to lead America, stating: “Please God don’t give this man the nuclear codes.”

Tony Schwartz, who claims to have ghostwritten the best-seller, has been a vocal critic of Mr Trump since the businessman decided to enter the presidential race, repeatedly voicing concerns over what might happen if he gains access to America’s nuclear weapons.

Mr Schwartz said he is advising the Hillary Clinton campaign for free as “penance” for helping Mr Trump’s success by ghostwriting the best-selling book.

Speaking ahead of the second Presidential debate, he told CNN: “This is my penance for having created a man who has become a monster, and I’ve spent 30 years feeling bad about it.

“Now I feel like I’ve got to show there’s nobody behind the curtain.”

When asked by the broadcaster if there was anything that he found appealing about Mr Trump, he replied “nothing”.

“This is a man who I really believe lacks a conscience at the deepest level, so there really was nothing. He was effective in certain ways, he’s a dominant, aggressive personality and he pushes and he pushes and he pushes and he gets a lot of what he wants.”

Donald Trump: Clinton should take a drugs test

Now the CEO of a consulting firm, Mr Schwartz describes himself as “The Art of the Deal ghostwriter now speaking out”. Mr Trump has, through his legal team, disputed the author’s position as the ghostwriter of the book, though Mr Schwartz claims to have proof from his publisher Random House that he authored the text in its entirety.

He regularly comments on Twitter on the Republican candidate’s conduct, recently stating: “Trump is totally willing to blow up the world to protect his fragile sense of self. Please God don’t give him the nuclear codes.”

He has commented on the allegations of sexual assault brought against Mr Trump, stating: “Nuts to believe Trump didn’t assault these women coming forward. They have 0 to gain and lots to lose. He lies for a living. Nauseating.”

He said Mr Trump’s statements on women are “exactly why I felt compelled to speak out about him,” and said in an earlier tweet: “Trump on groping women: this is exactly the man I knew. He considered women objects and that will never change no matter what Ivanka says.”

He has also suggested Mr Trump’s accusation that Hilary Clinton was on drugs during the presidential debate was a “projection” of his own behaviour, tweeting: “What’s funny about Trump saying Clinton was on drugs at debate is that he was the one snorting, jacked up, pacing the stage. Projection?”.

In July Mr Trump threatened Mr Schwartz with legal action following an interview he did with The New Yorker in which he stated: “If Trump wins and gets the nuclear codes, there is an excellent possibility it will lead to the end of civilisation.”

The author received a cease and desist letter from Mr Trump’s lawyers over his “defamatory statements” and demanded that he repay all royalties received from the book and a portion of his advance, in addition to providing a written retraction of his statements about the Presidential nominee.

Mr Schwartz’s lawyer responded by saying the author “will not be bullied into silence on this issue by outlandish and baseless legal demands”.