On the exchanges, Betfair has 2.44 (40.9%) on her quitting this year, 2.66 (37.5%) on her departing in 2019, 8.6 (11.6%) on her going in 2020, 13 (7.7%) in 2021 and 7.6 (13.2%) in 2022 or later. But this works out at combined odds of 78.4%, which is close to what I’d estimate as the 80%-85% odds of her quitting by the end of 2019, so I would have to recommend that you look elsewhere.
Interestingly, both Smarkets and Ladbrokes offer sharply differing markets on whether a vote of no confidence against the prime minister will be called in July. While Ladbrokes is offering 2/1 (33.3%) on a no-confidence vote being called, Smarkets is offering 2.92 (34.2%) on a vote not being called.
This means that you could make money by simultaneously putting money with Ladbrokes on “yes” and Smarkets on “no” for combined odds of (67.7%). Such arbitrage opportunities are very rare, so I’d advise you to grab this one fast, by putting £5.07 on “no” for Smarkets and £4.93 on “yes” for Ladbrokes.