Ed Miliband is fortunate that Britain is not America. As things stand, he would be heading for victory in a general election held this autumn. However were he fighting a US-style presidential election, then he would be staring at defeat.

For six months, Labour's lead has been fairly steady at around 10 points. All variations from this (including YouGov's latest poll for the Sunday Times, which reports a 5 point lead) can be explained by random sampling fluctuations.

However, over the same period, David Cameron has led Miliband by 9-10 points when people are asked who would make the best Prime Minister. A presidential contest would be likely to re-elect the incumbent.

YouGov surveys in the past few days for the Sun and Sunday Times show that the debit side of Miliband's ledger is longer than the credit side.

The good news for Labour's leader:
• He leads Cameron by two-to-one when people are asked is more in touch with ordinary people
• He also leads Cameron, albeit only narrowly, on being seen as honest and trustworthy
• His rating has improved since the beginning of this year. In mid-January, just 18% thought he was doing well as party leader, while 71% said he was doing badly. That represented a net score of minus 53. His rating is well up on those bleak days

One the other hand....

• He is still in negative territory, with twice as many people still thinking he is doing badly (57%) as well (28%)
• By large margins, Cameron is seen as stronger and more decisive
• 63% think Miliband has failed to 'provide an effective opposition to the government'. As many as 41% of Labour voters share this bleak view
• Only 25% think Miliband is 'up to the job of Prime Minister'. Even fewer, 19% (and only a minority of Labour supporters) reckon he 'looks like a Prime Minister in waiting'
• Just 23% say he 'has made it clear what he stands for'

There's no escaping it. Miliband has much to do, starting with this week's Labour conference, to seal the deal with the electorate. Labour's lead over the Tories is rooted in disappointment with the Conservatives and disillusion with the Liberal Democrats, not a positive view of Labour, or enthusiasm for its leader.

Does this matter? Can Labour really win in 2015 when its leader is so far behind his Conservative opponent?

As a rule, the popularity of a party and its leader march roughly in parallel. But not always. In 1979, Margaret Thatcher led the Tories to victory. Their margin of victory in the popular vote was 7%. But Gallup found that when people were asked who would make the best Prime Minister, Labour's James Callaghan outscored Thatcher by 43-30%.

We must be clear what this does and does not show. Plainly it is possible for a less popular opposition leader to turf out a more popular Prime Minister. However, it would be wrong to say that there is no connection between the two figures.

In the middle of the 1979 campaign, MORI found that the Tories led Labour by 5% (its figures were close to the final result) - but when the same people were asked how they would vote were Edward Heath still Conservative leader, the lead jumped to a whopping 18%. So at that time Thatcher was a drag on Tory support. Fortunately for her and her party, the outgoing Labour government was so unpopular that the Tories still won. With Thatcher their majority was 43; with Heath it might well have approached 200. Her personal popularity did not materialise for another three years, after the Falklands War in 1982.

YouGov's evidence is that Miliband is far less a drag on his party today than Thatcher was on hers in 1979. In our standard voting intention question we don't mention party leaders. When we add their names, Labour's lead generally slips by 2-4 percentage points.

Nevertheless, Miliband should still be worried. It is normal for government parties to recover from their mid-term rating. If that happens between now and 2015, then even a slight drag on Labour support could make the difference between victory and defeat. And it does not require the Tories to spend vast amounts on polls and political strategists to work out that they should spend much of the next election campaign encouraging personal attacks on Miliband. (I say 'encouraging' because if Cameron does this himself, he might come across as churlish and negative. Far better for the attack dogs to belong to the pro-Tory segment of the media than Tory ministers.)

To neutralise such attacks, Miliband must get his personal ratings up well before the next election. The potential good news for him is that if Labour is 10% ahead when its leader is still so unpopular, it could enjoy a much bigger lead were voters to decide that he is strong, decisive and up to the job after all.

See the full survey details and results here

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