Last week, Left Watch asked whether Cameron’s efforts to whip up interest in the Greens would actually hit Labour where it hurt most – the marginals.

This was difficult to determine, because the UK’s Green electorate had not received the sort of granular academic scrutiny that Rob Ford and Matthew Goodwin brought to UKIP’s supporters in Revolt on the Right.

Yet we spoke less than a week too soon, for today’s Observer carries a piece by none other than Ford himself providing a succinct but data-led overview of the Green threat.

Based on demographic surveys and local election results, he has produced a list of the 22 seats (all English bar Cardiff Central) with the highest shares of potential Green voters.

In addition to the Green’s own Brighton Pavilion these include seats narrowly held by both Coalition parties as well as four – Hampstead and Kilburn, Westminster North, Birmingham Edgbaston and Tooting – with slender Labour majorities.

Indeed Tooting has the second-highest share of potential defectors of all the seats listed, which might help to explain why Sadiq Khan is heading up Labour’s anti-Green task force.

Ford takes pains to point out that regardless of buoyant poll support the Greens likely lack the money and organisation to fully exploit their potential outside of well-known strongholds such as Brighton, Norwich and Oxford. But direct challenges are not the only way that Natalie Bennett’s party can hurt Labour in May.

Given the relatively small advance that Labour has made in the polls since 2010, any fresh fragmentation of the left-wing vote risks undoing the wave of Liberal Democrat defectors who have given Miliband what boost he currently enjoys.

This in turn could see well-entrenched Coalition MPs, especially urban Liberal Democrats with strong local machines, hold on to what until recently were seen as likely gains even on a reduced share of the vote, as well as bolster Tory prospects in already three-cornered fights like Watford where UKIP aren’t a major feature.

It might also see vulnerable individual Labour MPs toppled on election night even if the general trend is in Miliband’s direction.

The rise of the Greens as a viable alternative outlet for disaffected voters of the young, well-educated radical left also complicates Labour’s efforts to prevent the leakage of socially conservative working-class voters to UKIP, as it is almost impossible to please both sets of voters at once.

Thus whilst the Greens may not be the threat to Labour in 2015 that UKIP are to the Conservatives they may still leave Miliband ruefully eyeing a vital clutch of seats where the Green vote exceeded the margin of Labour defeat.