Eagle said she was trying to save Labour from doom as she prepared to announce formally her attempt to topple embattled leader Jeremy Corbyn -- a veteran socialist accused of lukewarm campaigning for Britain to stay in the European Union .
The ruling Conservative Party is also engaged in a fierce leadership battle over who will be the next prime minister after David Cameron announced his resignation in the wake of the seismic June 23 vote that has plunged Britain and Europe into uncertainty.
Interior Minister Theresa May, the current favourite against junior energy minister Andrea Leadsom, was expected to kick off her campaign on Monday with policy proposals aimed at appealing to disaffected voters who backed Brexit.
Conservative Party members will elect the new prime minister and the winner will be announced on September 9.
Labour Party members could be asked to do the same.
Corbyn has widespread support among party members but has lost the confidence of at least three quarters of Labour MPs.
The vast majority of the party's lawmakers do not believe Corbyn can lead them to a general election victory -- with the referendum on Britain's EU membership proving the last straw.