Ed Miliband faces poor polls and bad headlines

The transcript discusses the mounting pressure on Ed Miliband's leadership within the Labour Party, fueled by media speculation and internal dissent. Rumors suggest that former Home Secretary Alan Johnson might challenge Miliband if he signals readiness. Tristram Hunt denies reports of criticizing Miliband, while some MPs express a desire for leadership change. Despite denials from Miliband's camp, the media continues to portray a leadership crisis, highlighting the potential for rapid developments if a senior figure breaks cover.

What does the term 'critical mass' refer to in the context of the Labour Party's leadership?

What could potentially happen if a senior MP decides to break cover regarding Ed Miliband's leadership?