Comments from former Prime Minister David Cameron mean that almost every Conservative leader since Margaret Thatcher has now condemned Boris Johnson’s plans to override the Brexit treaty.
Speaking ahead of a crunch day in parliament, the former MP for Witney said he had “misgivings about what is being proposed.”
“Passing an act of Parliament and then going on to break an international treaty obligation is the very, very last thing you should contemplate, it should be an absolute final last resort”, he said.
The comments come after Michael Howard joined John Major and Theresa May in condemning the moves.
In a furious attack, he said: “Does [the minister] not understand the damage done to our reputation for probity and respect for the rule of law by those five words uttered by his ministerial colleague in another place on Tuesday – words that I never thought I would hear uttered by a British minister, far less a Conservative minister.
“How can we reproach Russia or China or Iran when their conduct falls below internationally accepted standards when we are showing such scant regard for our treaty obligations?”
Sir John Major also reacted angrily to Mr Johnson’s stance on international law.
“For generations, Britain’s word – solemnly given – has been accepted by friend and foe. Our signature on any treaty or agreement has been sacrosanct,” he said.
“Over the last century, as our military strength has dwindled, our word has retained its power. If we lose our reputation for honouring the promises we make, we will have lost something beyond price that may never be regained.”
According to reports Conservative rebels want former Prime Minister Theresa May to front an in-party uprising in parliament this week.
The bill is set to be debated by MPs today.