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Cyclists on the UK's roads travelled 3.1 billion miles last year and many will have done so with safety at the forefront of their minds. Lights and reflectors are a legal obligation after dark, and reflective jackets an increasingly common sight.

But it's the cycle helmet that is undoubtedly the most debated piece of kit. Helmets are not compulsory in the UK, unlike in Australia and parts of the US, yet the government encourages cyclists to wear one.

But is it really safer to wear a helmet when cycling?

Just a brief look at the blogosphere shows you what a hotly contested question this is. Unfortunately, the published evidence doesn't make the debate much clearer.

While many cyclists wouldn't leave home without clamping on their helmet, Dr Ian Walker, a professor of traffic psychology, has long believed head protection can work against someone on a bicycle.

Dr Walker . He found that for those wearing a helmet, motorists drove much closer when overtaking.

"In absolute terms they got 8-9cm closer than they did when I wasn't wearing one," he explains, "And the proportion of vehicles getting within a really close distance went up considerably."

He also decided to don a long, flowing wig to disguise himself as a female and found that drivers left him more space when passing. He says this further proves that drivers react to cyclists' appearance.

His findings have led Dr Walker to conclude that drivers use a cyclist's physical appearance to judge the specific likelihood of the rider behaving predictably. They alter their overtaking space accordingly.

He suggests drivers think helmeted cyclists are more sensible, predicable and experienced, so therefore the driver doesn't need to give them much space when overtaking. Non-helmeted cyclists, especially non helmeted "women" are less predictable and experienced, according to this study.

Skull protection

But it's not only motorists who alter their behaviour. Other research has looked at how helmeted cyclists take more risks, believing their head protection will compensate for this.

"I'm not convinced I saw any evidence of that," says Dr Walker. "I don't take any more risks when wearing a helmet and I think other cyclists would say the same."

A rejected all behavioural research, including that of Dr Walker, saying that none of the studies was robust enough to prove that helmets affect behaviour.

This Department for Transport report studied all the evidence available and concluded that "the effectiveness of helmets in single-vehicle collisions was estimated to be 50%".

But the report's authors admit that "it should be remembered that there was no specific evidence to support these estimates".

They do include a study into 100 police fatality reports which led them to say that helmets could prevent 10-16% of cyclist fatalities. But this was also an estimate based on a small study.

The problem is that the data available about injured cyclists, from the police or hospital admissions, does not record whether they were wearing helmets or not. It is therefore difficult to draw definitive conclusions in favour of helmets.

But for many cyclists, any such evidence comes second place to first-hand experience.

Angela Lee, chief executive of the Bike Helmet Initiative Trust and a nurse consultant in paediatric trauma, says it's clear that helmets make cycling safer.

"It's plain and simple that helmets are effective," Ms Lee continues. "If you think of people who have mobile phones, computers, I bet they all have covers on to protect them. You have a skull protecting your brain and if you know anything about computers you know that if you damage a computer you can't load the programme. That's exactly the same with your brain."

Wearing a helmet does seem like common sense - if it doesn't encourage you or other road users to take extra risks. But in the absence of really compelling evidence either way, it's up to individuals to make their own choices.

Me? I wear a helmet, and I'll continue to do so.