Could London tip the balance in the AV vote?
London voters could have a crucial impact on the outcome of the Alternative Vote (AV) referendum - but it may be less how they vote than how many bother to do so that counts.
Unlike elsewhere in the country there are no local elections in the capital on 5 May and some experts think as few as 15% of the capital's 5.7 million voters could turn out.
Expect a chorus of complaint about legitimacy if the Yes campaign triumphs on such a tepid mandate.
However, experts seem to be agreed that if Londoners - possibly quietly engaging with the debate on voting changes in a fashion undetected so far by opinion polls - do come out in greater force, then it could be decisive.
That the capital is both the No campaign's worst fear and best opportunity is clear.
Money has been poured in to a London-centric advertising and leaflet campaign.
The prime minister has "penned" his own direct appeal to Londoners and the Evening Standard, where his article appeared, has also backed the status quo.
Their target audience are the over-50s who are, they think, both most likely to vote and most likely to vote "no".
However, the complexity of London's political psyche makes things highly unpredictable and both the "progressive" tendencies of the capital, and the concentration of young voters in London, could swing things strongly the "yes" way.
Tony Travers, from the London School of Economics, spots the paradox that while younger voters are traditionally worse at turning out than older voters, they might confound this stereotype with important consequences on a single issue like this. Especially as it is one which purports to address a "cause" of/reason for their apathy and disengagement.
He says the younger you are, the more likely you are to want progressive votes, and young voters will associate AV with more progressive votes.
There is reason, too, to think there may be less instinctive resistance to change in the capital.
London was, and is, the base for the campaigns calling for fairer voting which made themselves heard on the streets of Whitehall as the Conservatives and Liberal Democrats thrashed out their coalition agreement.
It has been the focus too of protests among students, angered by higher tuition fees and the abolition of the Education Maintenance Allowance (EMA).
Yet all kinds of motivation could come into play which affect the outcome, not least the possibility that younger voters sublimate their desire for a change in the voting system to a wish to deny it to its advocate-in-chief Nick Clegg, using the referendum as an opportunity to punish the Lib Dem leader.
One of the claims of the No campaign is that the proposed new system is too complicated.
But Londoners have experience of a close-ish relation to AV - the supplementary vote system used to elect the mayor.
Here, all but the top two candidates are eliminated and their second preferences re-allocated.
There is also a partially proportional system for the London Assembly, a mix of constituency candidates and those chosen from a list, which has ensured minority party representation in London government.
On City Hall election days, voters have three ballot forms to fill in. It does not appear to have led to a collective head explosion!
Clearly, in its size and influence, the London electorate could yet make all the difference.