There are reports Theresa May could be forced to resign within days over her handling of Brexit.
One newspaper says 11 cabinet ministers have said they want her to move aside.
Her de-facto deputy David Lidington and environment secretary Michael Gove are said to be among those who could replace her.
Former Lib Dem minister Ed Davey says the UK needs a leader who can find unity.
We don’t comment in detail about security measures. We use different techniques - automated and manual - to identify and block signatures from bots, disposable email addresses and other sources that show signs of fraudulent activity. We also monitor signing patterns.
— Petitions Committee (@HoCpetitions) March 22, 2019
Meanwhile, the woman who started an online petition to stop Brexit says she's had death threats over the phone.
The 77-year-old says her Facebook account has also been hacked.
More than 4-and-a-half million people have signed it - making it the most popular on the parliamentary website.
