Rebel Conservative MPs believe the required threshold of 54 letters to the 1922 Committee may have already been reached.
The Guardian's Political Correspondent, Aubrey Allegretti, says some may have been swayed by seeing Boris Johnson face booing by crowds at the Platinum Jubilee celebrations.
IN: "I'm sure...
OUT: ...previously was."
DUR: 17 secs
http://www.fsnradionews.com/feeds/0606johnson-aa1.mp3