I'm not certain. I've just opened the market up for you and the rules set out as below tell you absolutely nothing!
"When will Theresa May officially cease to be leader of the Conservative Party?
Customers are entirely responsible for their positions at all times. Betfair will not be responsible for suspending the market when an official announcement is made by the Conservative Party. However, Betfair will suspend the market as soon as it becomes aware of an official announcement.
In the event of any ambiguity over an official announcement, Betfair may determine, using its reasonable discretion, how to settle the market based on all the information available to it at the relevant time. Betfair reserves the right to wait for further official announcements before the market is settled.
Betfair expressly reserves the right to suspend and/or void any and all bets on this market at any time in the event that Betfair is not satisfied (in its absolute discretion) with the certainty of the outcome."