I'd rank this as "possibly true, but I wouldn't bet too much on it". From what I can tell, there are no large, representative samples surveyed/studied in publications known for publishing high quality research.
One small/student sample study (2003) conducted at the University of Pécs (in Hungary) found a positive association:
we found that only long
and medium-length hair had a significant positive effect on ratings of
women's attractiveness; the other hairstyles did not influence the evaluation
of their physical beauty.
I also found a (pretty old, alas) narrative review (2005) on female attractiveness factors which didn't even include hair because it says there's wasn't enough research on that.
A multi-faceted study (2008) with a small sample "recruited opportunistically from a campus setting in Greater London" found (among other things) that
hair length had only a weak effect on ratings of attractiveness
And perhaps it's not only length itself that matters but other aspects of hair presentation. A 2015 study conducted in a "pedestrian areas of a town (around 60–70,000 inhabitants) situated on the south coast of Brittany in France" reports:
The confederate had long dark hair arranged in three different hairstyles: one with her hair falling naturally on her shoulders and her back, one with her hair tied in a ponytail, and one with her hair twisted in a bun. Results reported that the hairstyle had no effect on female passersby's helping behavior. However, it was found that the hairstyle influenced male passersby with men helping the confederate more readily when her hair fell naturally on her neck, shoulders and upper back.
It's easy to string up such small studies and conclude "OMG, there's an effect (even if it's weak)", but one has to be concerned with publication bias etc.
And regarding the poll in the question: this wasn't the newspaper's own poll, because it was explicitly reported in other venues as being conducted by TRESemme Philips, something that isn't all that clear in Daily Mail's reporting of the study. But I agree with Oddthinking's comment that a poll conducted by an company selling hair-care products presents an obvious conflict of interest. Also, from the newspaper reporting I can't tell what the methodology was. Even in the Hungarian (2003) study, they used the same faces with different (photoshopped) hairs. But I'm not sure that was done in the Phillips study. Usually Phillips puts out a press release on such things, which is often better written than the newspaper reporting thereof, but I cannot find their press release for this (2008) poll.
Alas it seems there's no systematic research on how cultural variations influence the perception of female hair length, so the best I can offer in that respect is some anecdotal evidence, which I may as well pluck from a newspaper:
"Short hair is still equated with masculinity," says Lesnik-Oberstein. "I have very short hair, and in England I often get mistaken for a man. It happened to me recently with two older ladies who mistook me for a man in the loo and said: 'Sir, this is a ladies' loo' very politely. They were mortified when I told them I was actually a woman. That never happens to me on the continent – for instance in Germany or Holland, where a lot of these societies are more egalitarian and matriarchal."
This may not be terribly relevant, but I'll still mention that a study on a large sample of people with fetishes and who necessarily discussed their fetishes on-line, found that
trichophilia (hair fetish) had a prevalence in this sample of about 7%, which ranked it 4th among body-part fetishes. Of course, this is far from being the prevalence of trichophilia in society/population at large. In comparison, in the same sample 47% had a foot/toes fetish, which was by far the most common body-part fetish.
My reasoning for looking at this last issue/study is that if there's some preference for some kind of hair in the general population, there are probably some individuals who exhibit it strongly enough to make it a fetish (for them). I'm not convinced that data from this last study is all that good though, because breast or buttocks fetishes were reported much lower (3% and respectively 2%) which seems counterintuitive and probably indicative of a strong selection bias in the sample.
