Sir John Major branded Boris Johnson a "court jester" in a furious assault on the "squalid" campaign for Britain to quit the European Union.
The Conservative former prime minister said he was "angry" about the "deceitful" claims being made by senior Brexit backers and accused them of "misleading" the public.
Taking aim at the former London mayor, Sir John said Mr Johnson would not have the loyalty of Conservative MPs if he becomes party leader.
The former prime minister has criticised Mr Johnson for trumpeting "depressing and awful" arguments.
Sir John described Mr Johnson - widely understood to have ambitions to lead the Tories - as a "court jester" and questioned his "late conversion" to backing Leave.
He told BBC1's Andrew Marr Show that the former London Mayor had the power to stop "fundamentally dishonest" Leave campaign claims on the economy and "squalid" arguments on immigration.
Sir John - a leading member of the Remain campaign - also attacked the Vote Leave lobby as a whole, saying: "They are misleading people to an extraordinary extent.
"They are feeding out to the British people a whole galaxy of inaccurate and frankly untrue information.
"And what they have not done is tell us what would be the position if we were to vote to leave."
He said there would be "chaos" if Britain voted to leave in the referendum on June 23, and claimed Britain would lose a "huge amount national income" through trade with Europe.
However, Mr Johnson defended the Vote Leave campaign, telling Mr Marr it was setting out "an agenda for the government to take back control" after leaving the EU.
He also criticised the Remain campaign for having no "long-term vision for the economy" if immigration continued at its current rate.
