The prime minister has resigned and said he will stay on as caretaker till the autumn, but that leaves very big decisions to be taken not only about who succeeds him but about the process for replacing him.I am told he rang Sir Graham Brady - chair of the 1922 backbench committee and de facto shop steward for Tory MPs - this morning. Yesterday, Brady told him he'd lost the confidence of the party and that he should resign. Johnson then refused and said he was determined to battle on.This morning he telephoned Brady and said that, having reflected overnight, he would be quitting after all.Which was simply the triumph of cold political facts over his determination to remain at Number 10 - namely that there has been an avalanche of resignations from his government.So when will Johnson's successor be chosen?That will be decided, probably on Monday, by the executive of the 1922 committee. One complicating factor is that its members are up for election on Monday!There is already a disagreement among Tory MPs about whether the leadership elections should start immediately - presumably next Tuesday - or should start after the summer recess in September.A source told me: "I think probably the election will be immediate. But there are some who think the party should have a bit longer to assess the candidates."The view, that longer is needed for the contest, is obviously favoured by lesser known candidates!Then a second decision has to be taken, jointly by the 1922 committee and by the Conservative Party Board, which is the timetable and geography for hustings for the contest, as and when the contest moves to its second phase.And to remind you, the contest has two phases. The first one sees Tory MPs choose their two favourite candidates, in a series of run-offs, over a couple of weeks. And then Tory party members decide which of the two should be crowned, over perhaps six weeks.The long and the short is the earliest a new leader could be chosen would be September. And it may be that there will be no new Tory leader till November.In other words, Boris Johnson will be leader for some time yet.Which begs a second question. Will all those 60 odd members of the government who resigned in the last 24 hours simply come back into government now that Boris Johnson is caretaker, or will he somehow have to find others to work for him on a temporary basis?It is still all very messy and uncertain.