Both were handcuffed while Ms Williams, a Commonwealth Games gold medallist, was searched for weapons and Portuguese sprinter Mr Dos Santos was searched for weapons and drugs.
Nothing was found during the search, a video of which went viral on social media at the time, and the Independent Office for Police Conduct (IOPC) began a misconduct investigation in October 2020.
The couple have publicly accused the Metropolitan Police of racism over the incident.
The officers involved – acting police sergeant Rachel Simpson and four constables named Allan Casey, Jonathan Clapham, Michael Bond and Sam Franks – face allegations they breached police standards of professional behaviour for duties and responsibilities and for equality and diversity.
On Monday, all officers appeared at a police misconduct hearing in south east London.
Disciplinary panel chairman Chew Yin Jones asked each of them: “Do you accept or deny that your behaviour on July 4 2020 amounted to gross misconduct?” Each of the officers replied with the word “deny”.
They could be sacked if gross misconduct is proven.
The hearing is scheduled to last until 27 October when an independent panel will decide whether to substantiate the accusations.
Gross misconduct is the highest disciplinary charge a police officer can face. If found guilty, an officer is likely to be handed disciplinary measures such as demotion, receipt of a written warning, or, in the most severe cases, termination from the police force.
At the time, the then-Met Police commissioner Cressida Dick defended the officers in question, stating that “any officer worth their salt would have stopped that car” and denying racism was involved.
Ms Williams told the Guardian at the time that she does not believe the “problem of racism” in the Metropolitan Police will not be addressed or tackled “under this commissioner”.
“It felt like there was a campaign led by the police commissioner to discredit us and shut down our complaint.”
Earlier, the couple had welcomed the misconduct hearing. “I welcome this decision and hope this opens the door for the Met to start being more honest and reflective about the culture of racism which is undoubtedly still a reality within the organisation.”
Mr dos Santos added: “This has been a long journey, and one which has not been easy.
“This sheds a light on how difficult it is to ensure the police are held responsible for their failings.”