The Metropolitan Police have released a video that they claim shows comparative stopping distances between a police mountain bike equipped with front and rear brakes, and one with no brakes at all.

The video was made public alongside a press release issued yesterday following the conclusion of the trial at the Old Bailey of cyclist Charlie Alliston.

But it raises a number of questions about the methodology used by the Met to conduct their stopping distance tests.

• Was the police rider an experienced fixed gear cyclist? A number of those who have watched the police video suggest the rider in the video does not appear to be experienced at riding that type of bike.

• Did the police test Alliston’s bike with and without a front brake to find out what the exact difference in stopping distances would have been?

• Did they test another rim braked bike with thinner road tyres? The police bike is heavier and has fatter tyres which should help it stop in a shorter distance than a lighter bike with thinner tyres.

• Did the police perform multiple runs to establish an average stopping distance?

Alliston, aged 20 and from Bermondsey, was acquitted yesterday of the manslaughter of 44-year-old Kim Briggs, who died from head injuries sustained as the pair collided on London’s Old Street.

However, he was found guilty of causing bodily harm by wanton and furious cycling, and could face jail when he is sentenced next month, with the offence carrying a maximum penalty of two years’ imprisonment.

> Charlie Alliston cleared of manslaughter of Kim Briggs but convicted of wanton and furious driving

It is unclear whether the video released by the Metropolitan Police is the same as one shown to a jury at the trial last week, and we are seeking clarification on that issue and the others raised above. As at the time of publication of this article, we had not received a reply.

During the trial, the Crown did not dispute that Mrs Briggs had stepped out into the road in front of Alliston.

Instead, one of the central pillars of their case was that his bike – a fixed-wheel Planet X track model – did not have a front brake.

Not only did that mean it was not legal for use on the road, but it was argued that if it had been equipped with one, he may have been able to stop in time, or at least that the collision, during which their heads clashed, would have been less severe.

While Alliston was described in court as a former courier – more recently, he has been working as a scaffolder – it is unclear how experienced or skilled he was at riding a fixed-gear bike, although it appears he had been doing so for at least a year before the fatal collision.

Caspar Hughes, who is on the co-ordinating group of campaign organisation Stop Killing Cyclists, told road.cc: “If Charlie Alliston had a front brake Kim Briggs might still have been here regardless of whether she looked before she walked out or not.

“But this terrible case highlights the double standards in how the national press report fatalities by drivers compared to people riding bikes.”

Hughes is a highly experienced fixed-wheel bike rider. He spent a decade as a cycle courier in London, before founding roller racing business Rollapaluza, which celebrates its tenth birthday this week.

We asked him his opinion of the distance it took the second cyclist to stop in the video.

He said: “It is hard to gauge how experienced the rider in the police video is at bringing his bike to a dead stop, but I know I can bring my bike to a halt much quicker than he did using nothing but the drive train.”

Evidence presented by the police at the trial suggested that Alliston had been riding at 18mph and was 6.53 metres from Mrs Briggs when she stepped into the road.

It was claimed that his braking distance was 12 metres but would have been 3 metres had his bike had a front brake fitted – something that Martin Porter QC, writing in the Guardian Bike Blog, said “is frankly absurd.”

Porter, a club cyclist and cycling advocate who has represented cyclists and their families in a number of cases, said that based on a formula in the book Bicycling Science by MIT emeritus professor David Wilson, the stopping distances here would have been 13.5 metres with no front brake, and 6.5 metres if one were fitted.

It’s worth noting, though, that in the police video, the first bike is indeed shown stopping after 3 metres, albeit from a slower speed of 15mph, and it is a different kind of bike to the one Alliston was riding and has two brakes.

Porter also made the point, as others have done, that the braking distance for a car being driven at 20mph – the location where the crash happened – is 12 metres, according to the Highway Code, and that in those circumstances, as well as in this case, reaction time also needed to be factored in.

> Husband of woman killed by cyclist calls for changes to law on dangerous cycling