The FT2 GP trainee, who has been at the forefront of recent calls from the medical profession for government action to end the ongoing NHS crisis, is understood to have been in the area for an interview nearby.
He told a Buzzfeed News reporter at the scene that he had rushed over to offer help after hearing screaming.
Dr Wijesuriya is believed to have helped to treat both police officer PC Keith Palmer, who died in the attack, and the attacker - shot dead by police officers responding to the incident.
Junior doctors chair
A BMA spokesman told GPonline that the junior doctors committee chair was not giving interviews at this stage.
Writing on Twitter hours after the attack, Dr Wijesuriya said he was 'humbled' by the response from emergency health and police personnel in the wake of the attack.
Home safe. Humbled by incredible efforts of paramedics, Met police & Hems. Thoughts with those in hospitals tonight receiving & giving care.— Jeeves Wij (@AskJeevesWij) March 22, 2017