UPDATE - 1 December 2009: A new poll in today's Independent further confirms the trend in public opinion against the Tories, since David Cameron's statement confirming he will not hold an EU referendum.
As the trend is enough to bring about a hung parliament, it's time for Mr Cameron to decide whether or not he wants to govern - and correct the EU referendum mistake that has triggered this downward spiral in public support.
A new poll published in yesterday's Observer has further stoked speculation that a recent reverse in public support for the Conservatives may bring about a hung parliament at the next general election.
Whereas last month's Ipsos-Mori poll saw a 7% jump in the Conservative rating, this month's results - following the announcement of David Cameron's new EU policy - shows a stark reverse.
The poll shows Tory support down by 6% and Labour up 5%.
A failure of either of the two main parties to win a working majority would put the EU-fanatical Liberal Democrats into a position of power to dictate policy in return for helping one or another govern.
Any deal with the Conservatives would very likely involve the chopping of EU-confrontational ideas like a UK Sovereignty Bill and the return of certain powers from the EU that David Cameron recently outlined.
Trust test failed
The Conservative party and its supporters would be foolish if they failed to notice how renewed predictions of a hung Parliament have started after David Cameron not only ditched a very public "cast iron guarantee" of a vote on the Lisbon Treaty, but contradicted his own stated principles by failing to pledge any replacement EU referendum at all.
Whatever technical arguments can be made in justification of his updated stance following the removal of the final hurdles blocking the Lisbon Treaty's ratification, Cameron's new policy totally fails the trust test.
Somehow, the Westminster Village consistently fails to recognise that this is the most damaging test of all to fail.
A large proportion of people wanted a say on the scale of the EU's powers and now the Tories have become just like the other parties in preventing us having one.
That's the supremely damaging message that will have resonated most strongly from Cameron's recent statement.
In a bizarre move for a party that at best can hope to win a small majority at the next general election, the significant support that comes with an EU referendum was just thrown away and no striking attempt was made to hold onto it.
The impact is now being seen in the polls. Predictably, the Conservatives are falling back into the low levels of trust and public support the other two parties have experienced since their own EU promise-breaking episodes.
But this emerging danger for Conservative prospects at the next general election can still be nipped in the bud - by a new EU referendum pledge.
But it had better come quickly, before momentum builds further in the wrong direction and it becomes impossible for Cameron to prevent near-triumph turning into tragedy.