The pollster's gloomy prognosis is that "Unless Nick Clegg can secure a new tranche of votes, from the centre and right-of-centre, Clegg's party seems doomed to suffer - certainly for as long as it is in coalition with the Conservatives".
The Kellner piece usefully distinguish between churn between the parties and the loss in net support. So YouGov calculate that Nick Clegg has picked up 600,000 voters who didn't vote LibDem in May but who would do so now - but that this is outweighed by the loss of allegiance of 4.7 million who did vote LibDem, but now wouldn't.
Two million May 2010 LibDems now intend to vote for Ed Miliband's Labour party, half a million for the Tories, six hundred thousand for others, while 1.3 million don't know, and around 300,000 wouldn't vote.
Labour has a net gain of 3.2 million voters. David Cameron's net loss of 0.7 million in year one may well be less than he feared given economic conditions, but he would be wise to anticipate having to increase his support substantially by the end of the Parliament to stay in office.
Among the greatest swingers of all against Nick Clegg's Liberal Democrats since the Coalition was formed are Guardian readers, who have been even more likely to desert the party than students, and who now favour Labour over the LibDems by a margin of 51 points.
You Gov reports Guardian voting intentions as follows, compared to May 2010:
Labour 66% (+24%)
LibDems 15% (-30%)
Conservative 7% (-)
Others 12% (+5) - including Greens 9% (+5)
A Labour moment indeed!
The Green party rise to 9% from 4% means that they have now overtaken the Tories as the third party in Guardianland on this poll.
(Just to clarify sourcing to avoid confusion: Kellner's Prospect piece reports findings are from YouGov's latest nationwide survey involving 50,000 people. While the Prospect graphic gives the change in vote share, the party shares behind them, and reported here, were provided directly by YouGov in response to Next Left's inquiry).
The LibDems have lost support with the readers of newspapers on the right too - though only 6% among Mail readers and 8% among Sun readers, where they of course began with much less to lose. They have dropped 15% among public sector workers and 18% among trade union members. It is more surprising is that the loss of Guardian votes outstrips even the loss of LibDem support among students, where the LibDems are down 25% and Labour up 19%. Nick Clegg might well think that life's not fair when he sees that his Conservative partners are up 5% among students: this suggests that he may have lost even those students who did agree with his u-turn to his partner David Cameron.
YouGov showed a 3% LibDem lead over Labour in May 2010 by 45% to 42%
However, contrasting May 2010 findings from other pollsters could cast doubt on the theory that the collapse in support reflects a bursting of a Cleggmania bubble among Guardianistas.
It may also be that the paper's readers were already considerably less taken by the prospect of a "liberal moment" last May than its editorial writing team, before becoming much more disillusioned with Clegg's party since.
One of the curiosities of the election was that The Guardian was the only national paper whose readers swung against the LibDems - according to the British Election Survey - despite it providing the first ever national newspaper editorial of the party, when the Coalition was little more than a glint in the eye of Cameron or Clegg, as we blogged previously:
Labour's slender two point (43-41%) lead over the LibDems among Guardian readers in 2005 extended to nine points (46-37%) in 2010, according to the tables in the Dennis Kavanagh and Philip Cowley British General Election of 2010.
One plausible hypothesis is that the Iraq war was considerably more important in switching Guardian readers from Labour to LibDem in 2005 than the newspaper's endorsement of the LibDems in 2010, when both the fading of the Iraq issue and the threat of a Tory government saw a shift back towards Labour.
There may be some consolation for Nick Clegg in a Prospect column from Charles Kennedy, though he ought not to get too excited by a headline "I've learned to love the Coalition" which does not really come particularly close to reflecting anything Kennedy writes in the text.
Kennedy does somewhat endorse the Coalition, having abstained on its formation, in expecting it to last the parliament, to the extent that he writes that "once the deal was done ... it is in everyone's interest that it succeeds", despite the LibDems having had "the rougher end" of it so far.
As for what that means for the Liberal Democrats when they next meet the voters, Kennedy frankly acknowledges that he does not know:
"The real fortunes of the party will hinge on the economic prognosis in the third and fourth years of this parliament. It is simply too early to tell what that will be".
We shall all have to wait to find out whether the cautious support or this 'wait and see' message turn out to be more significant in the end.