correct
He wanted to be PM of a UK that was in the EU
He thought 'leave' would lose
If they did, then Tory party rules dictate that only 2 candidates can ultimately progress to the membership for election to leader
The membership was where Boris was strong, but he needed to reach that stage to secure his ambition
If Remain won however, one of those candidates would be George Osborne
The only other wing of the party that could guarantee the voting bloc for the second candidate (100+) was the Eurosceptics
Boris therefore needed to join the Eurosceptic wing to secure their support for a leadership campaign
If he didn't join 'leave' they'd adopt someone else as their flag bearer, and he'd never reach the final shoot out
This is why he has a whole host of pro-European quotes attributed to him, why he took a week to make his mind up to join their campaign, why he wrote this piece in the DT over the weekend trying to row back the result, why Gove stood against him, and why he ultimately backed down himself
