Boris Johnson's options for the EU referendum – and their consequences

It's decision time for Boris. Having spent months - if not years - teasing David Cameron (and the rest of us) as to whether he is an 'outer' or an 'inner' the time is fast approaching when the Mayor of London and possible future Tory leader (and Prime Minister) will have to make up his mind which side he is going to back in the EU Referendum.

So what are his options and (more to the point) what are the consequences for him of making the right or the wrong call?

Boris calls for 'Brexit' - and the country backs Brexit too

This is the highest risk strategy for Johnson - all be it the one which gives him the greatest chance of fulfilling his ultimate ambition of becoming Britain's next Prime Minister. In this version of events the Mayor says (with heavy heart) that the deal David Cameron has negotiated is not good enough and so he will lead the campaign to leave.

This would electrify the referendum. It would pit Cameron against one of the most charismatic politicians of his generation and would fundamentally change the nature of the race.

In these circumstances if the country were to vote to leave then it is inconceivable that Cameron could stay on as Prime Minister and Johnson would be uniquely placed to succeed him as the head of a new Government outside of Europe.

Boris calls for Brexit - but the country says we want to stay.

This would be the worst of all worlds for Johnson's burning ambition. He would have staked his reputation on a 'leave' vote and been rejected by the voters. He would be punished by Cameron and left to languish on the backbenches. His electoral mystique would be shattered and his chances of succeeding Cameron would disappear. Johnson knows this - and that is why he is so reluctant to take such a big risk and nail his colours to Brexit.

Boris backs 'in' and the country backs 'in' too

This is really the status quo option - and the one that, if you were reading the tea leaves today, is the most likely. Under this scenario Johnson throws his weight behind whatever deal Cameron gets and then plays a prominent role in the 'in' campaign. If he does this Johnson will expected to be rewarded by Cameron for such a show of loyalty - and he may even have raised this issue with the Prime Minister already. He will want a big cabinet job like Foreign Secretary or Home Secretary that would help position him for the leadership election which will follow when Cameron eventually decides to step down. The last thing he wants is to be handed some political poisoned chalice like Health or Work and Pensions that would destroy his political credibility faster than you can say 'waiting times' or 'universal credit'.

Boris back 'in' but the country backs 'leave'

This is not ideal for the London Mayor - but it is not necessarily disastrous either. Because even if there is a 'leave' vote there will still be a Tory Government and there will be a vacancy for the top job. Boris is still the Tories biggest electoral asset and a leave vote would damage George Osborne's succession chances much more that those of Johnson. Given that Theresa May is also backing 'in' and there are few credible candidates among the avowed Tory leavers any contest would leave Johnson in a strong position to Britain's next Prime Minister.

So, all in all, the smart money is on Boris backing stay. But as we all know Johnson has made a career out of being unpredictable: And so, like David Cameron, we should rule nothing out.