NEW YORK, Feb 5 (TIWN): Boris Johnson has been rocked by another Downing Street resignation after a fifth aide quit as Cabinet ministers said they believe there is a '50/50' chance the PM will be forced out.

Elena Narozanski, a member of the Number 10 Policy Unit, resigned this morning, according to the Conservative Home website. 

Some senior ministers believe 'it feels like the end' after yesterday's exodus amid mounting fears in Downing Street that more staff and even ministers could resign. 

But the Prime Minister's allies have insisted the shake-up is actually evidence of Mr Johnson 'taking charge'. 

Senior Tory MPs today issued a fresh warning to Mr Johnson that he must 'shape up or ship out'. 

Number 10 was in meltdown last night as the PM ordered a brutal clearout in a desperate attempt to shore up his troubled premiership as Rishi Sunak primed himself for a leadership bid.

Downing Street announced that the PM's chief of staff Dan Rosenfield and private secretary Martin Reynolds will be leaving.

That announcement came after it emerged the PM's communications chief, Jack Doyle, was also departing. 

Mr Johnson had already been hit by the shock resignation of one of his closest allies, policy chief Munira Mirza, yesterday afternoon.