A cyclist accused of killing a woman by ploughing into her on a track bike shouted at her as she lay injured, a court has heard.

Charlie Alliston was allegedly riding at 18mph on a fixed-gear bike with no front brakes before he collided with Kim Briggs, a mother of two, as she crossed a busy road in central London in February 2016.

He is on trial at the Old Bailey in London charged with manslaughter and causing grievous harm by wanton and furious driving under the 1861 Offences Against the Person Act.

David Callan was walking along Old Street at about 12.15pm on 12 February last year when he looked up and saw the crash, according to a statement read out in court.

“I had my head down looking at something on my mobile phone when I heard a shout,” he said. “It was a loud shout and seemed like a male voice conveying urgency, like a warning or alert.

“It made me look up immediately, just in time to see a collision between a cyclist and a pedestrian. The cyclist flew through the air and the pedestrian fell at the point of impact.

“The cyclist clattered to the ground further down the road but quickly sprang to their feet and shouted something at the pedestrian as they took a step towards the pedestrian, who lay on the ground. It seemed like the same voice I heard immediately before the collision.” Callan said he saw others had come to the pedestrian’s aid, so he continued on his way.

Jurors heard that Briggs, 44, suffered “non-survivable brain injuries” and died in hospital a week later.

The bicycle allegedly ridden by Charlie Alliston when the accident happened.

Alliston’s “fixie” bike was not legal to use on the road without it being modified to add a front brake, jurors heard earlier.

In January last year, Alliston bought the £700 Planet X bike secondhand for £470, telling the vendor, William Ringwood, he used to be a courier and wanted to use it for track cycling.

Edward Small, a crash investigator who studied CCTV of the incident, concluded that Alliston, who was then aged 18, would have been able to stop and avoid a collision if the bike had been fitted with a front brake.

The defendant had been travelling at an average of 18mph before he noticed Briggs step into the road, jurors heard. He was a minimum of 6.65 metres (21.8ft) away when he swerved and tried to take evasive action.

Tests on a conventional mountain bike found a stopping distance of about three metres, but Alliston’s model had a stopping distance of about 12 metres, the court heard.

Cross-examining, Mark Wyeth QC asked Small whether there could be a margin of error in his calculations of Alliston’s average speed before he saw Briggs. The expert replied that any difference would only have been a “fraction of a mile per hour”.

Wyeth suggested to Small that Alliston had the right of way as the lights on the stretch of Old Street were green. He said Briggs could have avoided danger by using a pedestrian crossing less than 10 metres away. Small agreed.

Referring to Alliston’s previous work, his lawyer posed a hypothetical question: “I’m an experienced courier. I’ve got two years’ experience as a courier running around central London. I’ve been riding fixed-wheel bikes since 2014 and, whilst the bike is new to me, I’m very familiar with road bikes without front brakes. Would that put me in a better position to navigate hazards than a serving police officer?”

Small said there would not be much difference without brakes.

Wyeth said: “We have seen velodromes and seasoned athletes. One way the fixed-wheel bikes can be brought to a stop involves getting up out of the seat and [putting] down pressure on pedals to get that kinetic energy to come to a sharper halt than just a free wheel.”

He asked whether Alliston could be seen doing just that, and Small said he did not recall the defendant rising from his saddle.

Alliston, now 20, of Bermondsey in south London, denies the charges. The trial continues.