"If I am fortunate enough to win I’ll need four years to deliver what I’ve promised. And having put trust at the heart of this election, I would serve out that term in full."
The words of London Mayor Boris Johnson, shortly before narrowly retaining City Hall on May the 3rd this year. So that's it - he can't possibly quit early and head back to Westminster, can he?
Boris' pledge not to quit early isn't the only promise which might come back to haunt him. He told Channel 4 News earlier this year that being Mayor of London would be his "last job in British politics". C4's political editor Gary Gibbon grilled Boris six times on whether he'd stand as an MP again, he repeatedly insisted he wouldn't. As for being leader of the Conservative party, Boris said: "I cannot believe that anyone would offer me the leadership of my party, I certainly won't be seeking it."
But of course we've heard this sort of thing from politicians before, and are so used to them reneging on these kinds of pledges it's almost seen as normal. And anyway, under some scenarios Boris could line himself up for a safe Tory seat long after he's finished at City Hall, by which time nobody will care much what he's said in the past.
One caveat. Boris also made another pledge just before the London Mayoral Election - he said he'd resign if a third runway at Heathrow was given the go-ahead. That pledge is one of several reasons why David Cameron will almost certainly kick any decisions about the airport into the long grass after 2015, when on current performance he won't be in power anyway.
That distinct possibility of the Tories losing the next election is almost certainly what Boris is hoping for; such a defeat would mean David Cameron resigning as party leader, triggering a Tory leadership contest late in 2015.
On a procedural note, if Boris were to resign early as London Mayor, the legislation calls for a new election date to be set no later than 35 days after he announced his departure, unless Boris quits within six months of the next scheduled poll, which is in May 2016, in which case the law seems to be comfortable with London having no mayor for a bit.
Would it be untenable for Boris to simultaneously remain Mayor of London as well as sitting in the Commons? Not at all - Ken Livingstone overlapped in both roles for a year between 2000 and 2001. Sure, Boris would be seen as a lame-duck Mayor, but his supporters would argue that he'll be in that situation anyway, having pledged to not seek a third term at City Hall.
As for how Boris would get back into the Commons, the gossip for quite some time has focused on Sir Malcolm Rifkind's super-safe seat of Kensington and Chelsea. There's been talk that 66 year-old Sir Malcolm will be politely urged to move aside at the next election, or possibly soon after, and Boris will be parachuted in.
There are other seats where elderly Tories might be put out to pasture - surely 82 year-old Sir Peter Tapsell will permanently relocate to sunnier climes to top up his infamous tan - but the thinking is that Boris needs a London constituency to be credible.
But there's always the possibility of a shock departure. In any parliamentary term about half a dozen MPs die, sometimes quite suddenly. Two years into this term and we've already seen four MPs pass away or be forcibly removed for expenses crimes, for example. So the unexpected departure from this world of a Tory in a safe seat could easily force Boris' hand.
The difficulty for the party as a whole would come if Boris sought to enter Parliament in 2015 or shortly before. If the Tories look set to lose the next election, the spectre of Boris positioning himself as the next leader by jockeying for a Westminster seat would create a vicious circle, deflecting attention from Cameron's re-election campaign onto Tory infighting.
Quite who would stand as Tory candidate for London in 2016 to replace Boris is a fairly open book. Zac Goldsmith, the MP for Richmond, is often touted. He's also pledged to quit as an MP if a third runway goes ahead and as such has a fairly easy get-out clause if it does.
But these calculations can't be made in isolation - although former Home Secretary and old-school Notting Hill boy Alan Johnson is often touted, there's also talk of the Tottenham MP David Lammy becoming Labour's candidate in 2016 and Goldsmith would look very white and upper class by comparison.
There's every chance of Oona King running again, which would pose similar problems for Goldsmith. Some talk of the media-savvy MP for Corby Louise Mensch becoming the Tories candidate.
Under this scenario Boris is ensconced at Westminster by 2015 or shortly thereafter. The Tories could win the next election outright, but that's a massive uphill task as they'd need to increase their share of the vote on 2010, which would be unprecedented in modern times. But assuming that happened we could be looking at either David Cameron departing with dignity in 2017 or 2018 and Boris emerging victorious from a leadership contest.
The alternative is something far more messy; the Tories win in 2015, but with Boris back at Westminster the plots and calls for Cameron to be swiftly despatched quickly grow. It only takes 15% of Tory MPs to express no confidence in a leader to trigger an election, and unlike Labour, the Tories have plenty of form in terms of palace coups.