He is standing as a Tory, as I understand it.
He resigns forcing a bye election, then is selected by his local party as the candidate.
Side issue: I'm sure they've reseached this, but as I understand it MPs can't resign. They take one of two nominal posts officially not consistent with being an MP ("THe Chiltern Hundreds" and another one) which gets them the sack. So he gets the sack, then gets himself selected as the Tory candidate for the bye election. However, you hold the Chiltern hundreds until the next resignee comes along, so in order to allow him to stand, someone else must have to resign. As I understand it.