Show Hide image UK 28 July 2014 Boris could be mayor and an MP - but he couldn't be mayor and Tory leader The London mayor would be forced to break his "solemn vow" to serve a full term were he to become leader of his party. Sign up for our weekly email * Print HTML Will he or won't he? Time is running out for Boris Johnson to decide whether or not he stands for parliament next year, with all agreed that a decision must be made before the Conservative conference. A YouGov poll in today's Evening Standard shows that just 37 per cent of Londoners believe it would be "reasonable" for him to become an MP (down from 43 per cent last October), while 43 per cent believe it would be "unreasonable" (up from 39 per cent). Boris's allies have long argued that he could wear two hats at the same time, as Ken Livingstone did when he remained the MP for Brent East during his first year as mayor (and he has been careful to never rule the option out). But should the Tories be defeated, with Boris standing in the subsequent leadership election (his principal motivation for returning), the situation would become more complicated. It is inconceivable that he could serve as both Conservative leader and Mayor of London for any significant period of time, leaving him with three options: to avoid standing in 2015, to persuade the party to delay any contest (if Boris stands down a minimum of six months before the end of his term, his deputy takes charge), or to trigger a costly mayoral by-election. Were he to resign as mayor, he would break his "solemn vow" to serve a full second term. He said before his re-election in May 2012: "If I am fortunate enough to win I will need four years to deliver what I have promised. And having put trust at the heart of this election, I would serve out that term in full. "I made a solemn vow to Londoners to lead them out of recession, bring down crime and deliver the growth, investment and jobs that this city so desperately needs. Keeping that promise cannot be combined with any other political capacity." The abandonment of this pledge would leave him exposed as a shameless liar (not a good start to his prospective leadership). The move would also do damage to the Tories, who would be accused of disrespecting the mayoralty and would struggle to avoid defeat in the capital. It is for these reasons, you suspect, that Boris is still dithering. › The FA needs to start acting like a national football association George Eaton is political editor of the New Statesman. Subscribe from just £1 per issue More Related articles One good thing about Brexit: the end of “honest conversations” about immigration Will Self: I was no fan of New Labour – but Brexit requires original thinking Corbyn can't provide If the government can back down on self-employed taxes, why not disability benefit cuts?