Beware of the betting odds for two reasons:
Firstly if reflects what the bookies have in liabilities for the various options. If they have a load of money on option (a) they will shorten the price but offer a better price on option (b) in an attempt to balance their book.
But more importantly I think “The next PM” means the PM after Mrs May. If the Conservatives win the next election (with her still as leader) she will not be the next PM. She will be the same PM as we currently have. To demonstrate this, if you look at Coral’s prices for the next General Election they ask 4/5 for a Conservative majority and offer 11/2 for a Labour majority. (This is nothing to do with “free” bets to attract new business. These are simply their current ordinary odds). This ties in nicely with the 5/1 they offer for JC to be the next Premier. It seems when taking all the odds into consideration that the bookies believe a Conservative victory is the most likely outcome of the next GE with Mrs May at the helm. So much so that they offer longer odds on other Conservatives taking the reins than they do on Corbyn moving into No.10.
To illustrate that there is more than the simple binary choice that seems to be suggested, you could put £56 on a Conservative victory and draw over £100 if successful and you could put £16 on JC becoming the next Prime Minister and draw over £100 if successful. So if it was a simple choice between JC becoming PM or a Conservative victory you could lay out £72 and be sure of walking away with £100. Bookies, as you can imagine, don’t work like that!