The arch-Remainer – who accused Boris Johnson of throwing a top diplomat “under the bus” – joins Chancellor Philip Hammond and Justice Secretary David Gauke
Sir Alan Duncan today resigned as a Foreign Office minister as top Tories mount an exodus to avoid serving under Boris Johnson .
The arch-Remainer quit days after he furiously accused the next Prime Minister of throwing Britain’s US Ambassador “under a bus”.
In his resignation letter, obtained by The Times, Sir Alan Duncan said Brexit had been a “dark cloud” over Theresa May’s Government.
He added: “It is tragic that just when we could have been the dominant intellectual and political force throughout Europe, and beyond, we have had to spend every day working beneath the dark cloud of Brexit.”
The 62-year-old spoke out earlier this month when Mr Johnson refused to say the UK Ambassador to Washington, Sir Kim Darroch, could keep his job over cables branding the White House “inept”.
Sir Kim quit hours after Mr Johnson failed to give his reassurance.
Sir Alan said Mr Johnson was guilty of “contemptible negligence” and had “thrown this fantastic diplomat under the bus to serve his own personal interests”.
“I’m upset and angry,” he said. “Boris Johnson has basically thrown our top diplomat under the bus.”
It comes as Mr Johnson – set to be confirmed as Tory leader tomorrow morning – faces the prospect of long-serving ministers opting to jump ship rather than sit in his Cabinet.
He is expected to draft in a host of hard right, anti-EU loyalists as he braces to leave the EU deal or no deal on October 31.