The political backlash unleashed by Brexit saw pro-Remain Tories scramble to unite behind a candidate strong enough to try to stop Boris Johnson becoming prime minister.
At the same time, the Labour revolt against Jeremy Corbyn gathered pace.
With both major parties still reeling from the shockwaves of the surprise - and narrow - victory for quitting the EU, the prospect of a snap autumn election sharply focused attitudes as leadership clashes loomed.
Home Secretary Theresa May was consolidating her position as the main potential "Stop Boris" candidate, as Europe piled pressure on David Cameron to go before his stated departure date of October so that tough talks on the Brexit "divorce" deal can begin in earnest.
With the race for the Tory crown expected to move up a gear this week, with the backbench 1922 committee set to outline the time table for the contest, allies of Chancellor George Osborne moved to dismiss claims he was attempting to change party rules in a bid to damage Mr Johnson's chances.
Allies of Mr Osborne dismissed claims in The Sunday Times that he was manoeuvring to ensure a woman had to be one of the two candidates selected by MPs who then go on to a leadership run-off decided by party members.
"He has not discussed rule changes with anyone," a source said.
Labour was also facing into a tumultuous week as anti-Corbyn rebels pressed-on with plans to force a vote of no confidence in the leader.
Former shadow education minister Tristram Hunt wrote in The Observer: "If Labour cares about Labour voters, we need to do something about the leader."
Mr Corbyn has made it clear he will fight any move against him from MPs and rely on the backing of grass root party members if it comes to a leadership challenge.
With many Labour MPs claiming that Mr Corbyn led a weak campaign to keep Britain in the EU, The Observer reported that shadow foreign secretary Hilary Benn was canvassing for support in order to try and force Mr Corbyn from office.
Leaked Labour Party research shows internal polling reveals that almost one in three voters who backed it at the 2015 general election would now support a different party, according to The Observer.
As the Tory tussle to replace Mr Cameron intensified other potential candidates made pointed interventions with Education Secretary Nicky Morgan warning in The Sunday Times that a Brexiteer-style tough stance on immigration would see the party thrown back into the "wilderness" if it went back to an "ideological comfort zone" in order to "appease the noisy fringes".
And Work and Pensions Secretary Steve Crabb said in the same newspaper: "The referendum campaign highlighted deeply entrenched divisions in parts of Britain's society which demands a One Nation response focused on improving social mobility and breaking down barriers to opportunity."
With the EU growing increasingly impatient with Mr Cameron's instance to leave Brexit talks to his successor, French foreign minister Jean-Marc Ayrault suggested he could be replaced in Number 10 within days.
A new poll showed that even if if the EU offered further reforms to the UK, the Brexit vote should hold.
Half of voters would stand by the result in such a scenario, while 39% would favour a second referendum, according to a ComRes survey for the Sunday Mirror.