Opinion Poll graphicThe Conservatives have plenty of polling headaches.

As Tim Montgomerie wrote yesterday, the suspicions aroused by the Tory brand haven’t gone away despite the much-heralded detoxification project, and ComRes found two weeks ago that while people put the Conservatives ahead on improving the economy, we still lag behind Labour on the question of who people think is best for their family.

Underlying those numbers is the awareness that the failure to make boundaries fairer means Labour have an in-built electoral advantage, too.

But despite those woes, the polling picture overall is starting to improve.

This week, Labour Uncut warned Ed Miliband that Labour’s poll lead over the Conservatives has drastically narrowed since the start of the year, and:

“…while there may be fluctuations (particularly around next year’s Euro elections), don’t expect too much of that already-shrinking 5% comfort blanket to be left by May 2015.”

YouGov’s poll for The Sun startled a few people when it found the lead had fallen to 1 per cent on Tuesday. That may have just been a blip, but the general trend seems to be one of a shrinking distance between the two main parties – YouGov’s other lead numbers this week, 4 per cent, 5 per cent and 4 per cent, are a far cry from the 10+ per cent leads Miliband enjoyed at the start of the year.

Of course, short term fluctuations aren’t definitive – long term trends are more telling.

YouGov’s Joe Twyman analysed the data and produced this graph of Labour’s poll lead since the start of the year:

Labour lead YouGov

That black line is bad news for Miliband, dragging him inexorably downwards. His own efforts don’t seem to be bumping his numbers up in any permanent way, while the Government’s successes are apparently winning votes.

That isn’t to say the election is in the bag .Events, as ever, may intervene. The brand problems Tim discussed still deter voters who ought to be potential Tories. UKIP’s impact in marginal seats could still let Labour into Downing Street. Plus, the pitch we are playing on is skewed in Miliband’s favour.

But it’s hard to look at Twyman’s graph and not conclude that Labour’s lead is as solid as a waxwork in a furnace. If Cameron can turn the heat up by winning the argument with the Lib Dems to scrap green taxes, demonstrate further progress on reducing crime, continue the return to economic growth and hold his party together in support of James Wharton’s In/Out EU referendum,  it may melt away altogether.