Two police officers racing to the scene of the Streatham terrorist attack are under criminal investigation after one of their cars crashed into vehicles belonging to the public.

The Independent Office for Police Conduct (IOPC) issued the notices for alleged dangerous driving, which is a potential criminal offence, and gross misconduct, which is a potential offence under police discipline rules and can be punishable by dismissal.

Both are male, armed Metropolitan police officers, who, as a result of the decision by the IOPC, have been placed on restricted duties, meaning they cannot drive.

The Metropolitan Police Federation (MPF), the force’s staff association, called the decision a “joke” and said the watchdog should rethink its decision.

On 2 February, one officer who was driving an unmarked car was involved in a crash with two vehicles driven by members of the public as he headed to the scene of the stabbing in south London. Two members of the public were injured, the Met said.

The other officer, who was driving a marked armed response vehicle and not involved in the collision, also went to the scene.

The two police cars were travelling in convoy with flashing blue lights and two-tone sirens when the crash happened, the MPF, representing the men, said.

Armed police surveillance officers were monitoring Sudesh Amman, 20,who had recently been released from Belmarsh prison for terrorism offences. It was feared he was so dangerous he could stage an attack.

Amman stabbed passersby on Streatham High Road and was shot dead by the surveillance officers; colleagues were called to give assistance.

A spokesman for the IOPC said: “We are conducting an independent investigation into a road traffic incident involving a Metropolitan police car which collided with two vehicles while responding to the terror attack in Streatham on Sunday 2 February. Two people received injuries.

“On Friday 28 February we served notices of investigation for dangerous driving and gross misconduct on the officer driving the vehicle involved in the collision and on the driver of a marked police vehicle which was in close proximity to the unmarked vehicle but not involved in the collision.

“A criminal investigation does not mean that criminal charges will necessarily follow. Misconduct notices do not imply guilt but are to inform the officer that their behaviour and conduct are under investigation and [of] the level of severity. Such notices are not judgmental in any way.”

Ken Marsh, the chair of the MPF, said: “The public will be appalled when they hear that brave police officers responding to a terrorist attack can be treated in such a manner. What kind of message does this send? These officers and their colleagues put their lives on the line that day to protect the public. Now potentially their careers are on the line. It’s absurd. A complete joke.

“Our colleagues did not know what danger they were travelling towards as the information emerged in real time about stabbings and threats of a suicide vest and explosives. Yet without hesitation they drove towards that danger. Because that’s what police officers do.

“And yet now their careers are at risk as the hindsight brigade decide to justify their existence. These people need to understand the split-second and dynamic decisions police officers have to take.”

There has long been tensions between sections of the police and the IOPC. Some officers think investigations take too long, with many kept in limbo for years fearing they could lose their jobs. The watchdog thinks officers exaggerate fears of being persecuted and believes the notices of investigation it issues are necessary to protect officers’ rights.

Marsh urged the IOPC to think again. “No one is saying that police officers should not be scrutinised or that their actions should not be accountable,” he said. “But the last thing officers responding to a terrorist attack should be worrying about is whether their prompt response and bravery will put their livelihoods in danger.

“We are of course supporting our colleagues at this very difficult time and call on the IOPC to think again about what they are doing and what message their actions send to police officers.”

The Met said: “On Friday 28 February the IOPC served notices of investigation for dangerous driving and gross misconduct on the driver of the vehicle involved in the collision and on the driver of a marked police vehicle. The driver of the marked police vehicle was in close proximity to the unmarked vehicle but not involved in the collision.

“The officers have been removed from driving duties pending the outcome of the IOPC investigation. They remain on firearms duties.”

The IOPC investigation into the shooting of Amman continues, with officers being treated as witnesses.