The Republican presidential candidate Donald Trump has "no conscience", and is "sociopathic", according to the man who knew him inside out when writing the Republican candidate's book, The Art of The Deal.

Tony Schwartz, who now runs a high profile consultancy company, the Energy Project, is a fast-talking Jewish New Yorker who was hired by Mr Trump to work for him in 1985 after the writer had repeatedly drawn attention to his failings in articles for the New York Times.

To write The Art of The Deal, Mr Schwartz spent 18 months with Mr Trump at close quarters. The book was a smash-hit and largely made Mr Trump's reputation. Mr Schwartz, for his part, went on to other ventures and only began criticising Mr Trump when he realised that the property tycoon had convinced himself that he had written the book.

Speaking to Kirsty Wark on BBC Newsnight last week, Mr Schwartz said: "Trump has no social graces whatsoever, they are utterly absent."

He added: "I created a version of Donald Trump far more appealing than he actually is. I absolutely feel the need to atone for that, and that's why I am speaking out now."

On Friday, Mr Schwartz spoke at the Oxford Union and then attended Shabbat dinner with 200 students at the Slager Jewish Student and Community Centre, run by Oxford Chabad. Rabbi Eli Brackman, who runs the centre with his wife Freda, said: "We were absolutely thrilled to have Tony Schwartz come to join us in a warm and friendly Jewish atmosphere. He was very happy to be here, he spoke and then took questions from the students."

At the Oxford Union, Mr Schwartz noted: "The reason I'm speaking out is to show Trump voters that he doesn't care about them - he only cares about himself… More than any human being I have ever met, Trump has the ability to convince himself that what he is saying is the truth."