Outspoken backbencher Nadine Dorries, who is set to join the Leave campaign, has said she hopes the Prime Minister quits Downing Street as soon as he loses the referendum.
The once-in-a-lifetime ballot on Britain”s membership of the Brussels club will take place on June 23.
Mr Cameron is set to meet with EU leaders on the day of the referendum – with a result expected in the early hours of the next day.
But in a radio interview, Ms Dorries said she could not foresee Mr Cameron surviving a defeat.
She told LBC: “If the British public vote to leave the EU, I would imagine and hope the first thing David Cameron would do is stand down.”
The former I”m A Celebrity star, who once dubbed the Prime Minister “a posh boy who doesn”t know the price of milk”, also slammed Europe”s flatlining economy.
She said: “I don”t want my children limited to a narrow European Union whose economy is in decline.”
The Mid-Bedfordshire MP”s uncompromising stance contrasts with other Tory Eurosceptics, who claim the embattled PM should stay on even if voters reject his new deal.
However, many admit privately that his position would be untenable – clearing the way for leadership challengers such as the chancellor George Osborne and London Mayor Boris Johnson.
All six pro-Brexit cabinet ministers – including justice secretary Michael Gove and work and pensions secretary Iain Duncan Smith – have said that their leader should stay on to negotiate Britain”s terms of exit from the EU.
Mr Cameron himself has argued that the referendum is not about “this politician”s future or that politician”s future”.
Dismissing the prospect of an early departure from Downing Street last month, he said: “My authority depends on holding the renegotiation, holding the referendum.
“That is what I promised, that is what I must deliver.”
The Prime Minister has secured a range of concessions from EU leaders ahead of the historic vote – but critics have said the deal does not go far enough.
Migration Watch UK chairman Lord Deddes has said: “This deal will do virtually nothing to reduce mass immigration which is the public”s greatest concern.”