Briggs, a 44-year-old HR consultant was on her lunch break when the collision occurred. She suffered “catastrophic” head injuries and died in hospital a week later.
Alliston, who was riding a fixed wheel track bike with no front brake, which is not legal on the road, is said to have shouted at her as she lay mortally injured, later blaming her for the collision in posts online.
Prosecutors claim he could have avoided a collision had a brake been fitted.
But Alliston, now 20, claims he had no idea it was a legal requirement for a front brake, insisting it would not have made any difference when he saw Mrs Briggs come into the road with a mobile phone.
“I tried to go around,” he said.
“Having a brake, I wouldn’t have had enough time to pull it.
“It was a few split seconds prior to the impact, which caused the impact, so a brake at the time wouldn’t have made a difference.”
Alliston, from Bermondsey, is on trial at the Old Bailey where he denies manslaughter and causing bodily harm to Mrs Briggs by “wanton or furious driving” under the 1861 Offences Against the Person Act.
Alliston took to the witness stand on Thursday wearing a white shirt and jeans.
He said he had worked as a courier for three different companies based in central London for around six to eight months from mid-2015, having dropped out of sixth form, where he was studying photography and business studies.
He told jurors he used the same Cinelli brand fixed-gear road/track bike, which was not fitted with a front brake when he bought it, making around 20 deliveries a day.
He said he did put a front brake on the cycle “at times”, but was never made aware of the legal requirement for it, adding he never had an accident in the course of his work.
His barrister, Mark Wyeth QC, asked: “Were you aware at any point in your life up to the collision on February 12, 2016 that there was this regulation that ‘fixies’ had to have a front brake?”
“No,” said Alliston.
In January last year, Alliston bought a £700 Planet X bike second-hand for £470 telling the vendor he used to be a courier and wanted to use it for track cycling.
By the day of the collision Alliston was working for a scaffolding firm.
“I was intending to get food from Shoreditch for me and my girlfriend, but something came up, so my girlfriend asked me to waste time for 30 minutes.
“I have then gone left into Shoreditch and come onto Old Street,” he said.
“I was cycling at a safe and reasonable speed personal to myself. I was capable at the time of controlling it.”
Alliston said he shouted twice after spotting Mrs Briggs.
Asked why he shouted, the defendant replied: “To make the pedestrian aware of my presence so they were aware if they were to then cross the road.”
He said he directed a second shout towards Mrs Briggs and slowed down as he approached her and manoeuvred his bike to avoid her.
Alliston said: “After the collision I just jumped straight back up to my feet, turned around, saw what happened and then went blank.”
He added:” At the time of the accident I believe I did see Mrs Briggs come out onto the road with a mobile in her hand.”
Jurors were told that Alliston talked of removing his front brake from his Cinelli bike in a tweet in February 2015, comparing the experience of riding it to being in a “Lucas Brunelle movie”.
The court heard that the stunt cyclist makes “alleycat” videos, in which he rides around cities including London “doing dangerous stuff” such as weaving in and out of traffic, narrowly avoiding pedestrians and going into bus lanes.
But Alliston, who admitted to not wearing a helmet, denied copying the film-maker, or enjoying taking risks.
“I wouldn’t say I drove recklessly or at any time dangerously,” he said.
“At all times I would know what I’m doing and completely responsible for my actions.”
He added: “I did not get a kick or enjoyment out of not being safe.”
Prosecutor Duncan Penny QC, cross-examining Alliston, suggested “fixies” are popular in urban areas such as Shoreditch, where some riders view them as “stylish”.
He asked Alliston: “It’s far from uncommon for people riding track bikes or ‘fixies’ without front brakes to not wear a helmet. It’s part of a look, isn’t it?”
The defendant said: “It’s not necessarily down to a look. It is the rider personally.”
Alliston denied the Planet X bike he was riding on February 12 last year was responsible for the collision with Mrs Briggs.
Mr Penny suggested: “The characteristics of that bike and the ability to stop are such that you didn’t have enough time to avoid the collision with Mrs Briggs because of the characteristics of that bike.”
Alliston replied: “Not because of that bike I was unable to stop, no.”
Mr Penny said: “I’m suggesting to you that, had you had a front brake, or rather been on a bike which did have a front brake, that could or would not have happened.”
Alliston said: “No. I feel, regardless of whether the brake was on the bike, it would still have happened.
“I did everything, to be honest, I needed to in the situation.”
Mr Penny continued: “Is your position, had you been on a butcher’s bike, with the world’s best brakes, this would still have happened?”
“Yes,” said Alliston. “I made the necessary adjustments to my speed.”
On the day of the crash, Alliston posted a comment on an online news article, claiming: “In no way whatsoever was this my fault.”
He later wrote on an internet forum for fixed bike enthusiasts, how he twice warned Mrs Briggs to “get the f*** outta my way,” jurors were told earlier in the trial.
“It is a pretty serious incident so I won’t bother saying oh she deserved it, it’s her fault. Yes it is her fault but no she did not deserve it,” he wrote.
“It’s not my fault people either think they are invincible or have zero respect for cyclists.”
The prosecutor described the comments in court as “pretty unattractive”, but Alliston denied it was a show of “bravado”, adding: “I do hold my hands up and admit everything that got said in that time was stupid and not thought through, and it was not meant.”
The trial continues.