Footage being circulated on social media shows a Volkswagen GTi being pushed down Western Avenue, A40, by the delivery vehicle with other cars honking their horns to get the attention of the driver.
Eventually, the driver stops with motorists shouting at him: “What the f*** are you doing man?!”
The driver appears astonished to see the car in front of his truck, claiming he did not see it, or know it was there.
He can be heard yelling: “I didn’t see him, I honestly didn’t see him.”
He later tells the driver of the car: “Let’s pull over and I can explain.”
Goulding revealed on Instagram that her driver, Guy, was one of the motorists who stopped to help, with Ellie herself checking on the driver of the car.
She told her 14.4 million Instagram followers: “On a side note, I can’t believe the first instinct of the other drivers who got out was to instantly start filming on their phones and shout abuse at the poor shocked driver, not even checking the other driver was okay.
"What on earth.”
A Royal Mail spokesperson said: “We are very concerned about this incident.
"We sincerely hope that no one was hurt.
"We are investigating as a matter of urgency.”
Metropolitan Police said a routine patrol car came across the crash at 10am, close to the Greenford roundabout.
A spokesperson said: “There were no reported injuries.
“Officers spoke with both parties.
"No arrests were made.”