Donald Trump “could be in violation of the US Constitution the moment he takes the oath”, the White House’s former chief ethics lawyer said.

Norman Eisen, who served as Special Envoy for Ethics and Government Reform during Barack Obama's first term, said he could not see how Mr Trump could serve as President while he had such a large business empire with links to overseas regimes.

Under the Article 1 of the US Constitution, members of the federal government are forbidden from accepting gifts from foreign governments unless allowed by Congress – but there is some debate about whether this applies to the president.

Last week, questions were raised by many over the potential conflict of interest Mr Trump’s election posed, with the Washington Post reporting his company concluded eight deals tied to a hotel project in Saudi Arabia – which is ruled by a theocratic monarchy – during the campaign.

He also appears to have paid up to $10m to have the name Trump Tower put on a luxury hotel in Istanbul, Turkey.

The owner of the hotel reportedly has links to the Turkish government under President Recep Tayyip Erdogan who has been widely criticised for his brutal crackdown on dissidents following an attempted coup in July.

Mr Eisen described the situation as “like a hostile takeover of the United States government by the Trump Organisation”.

He said: “It’s profoundly concerning. He could be in violation of the constitution the minute he takes his oath.

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“I don’t even know how he can take his oath when the payments are flowing to his hotels.

“It’s in his oath: ‘I’ll defend the constitution’ and as soon as he becomes president he will be undermining it.

Mr Eisen said the only way for Mr Trump to take office legally is to put his companies into a blind trust to be managed by an independent trustee who can buy and sell his assets without his knowledge or input.

He explained: “The president loves to say that he is going to build a big beautiful wall, he needs to build a big beautiful wall of trust.

“The trustee would take the proceeds of business and put it behind the wall and buy and sell investments that are unknown to Mr Trump.”

During the campaign, Mr Trump suggested he would hand over control of his business empire to his three adult children but this was thrown into question last week when it emerged his daughter Ivanka had attended his first meeting with Japanese Prime Minister Shinzo Abe.