An electric car owner has claimed her vehicle’s autopilot engaged without warning and accelerated to 65mph, zigzagged across the road and caused a serious crash, the Guardian can reveal.

The alleged incident involved a doctor, Ravpreet Kaur, who was travelling in Buckinghamshire with her son in the family’s £80,000 BMW iX. Her husband said they were lucky to escape unhurt.

The manufacturer has strongly disputed the claims, insisting that an investigation had found nothing wrong with the car.

This latest claim has emerged four weeks after Brian Morrison, from Glasgow, said he had been “kidnapped” by his electric MG.

In that incident, he said his car would not slow down from 30mph or turn off, forcing him to do a controlled crash into the back of a police van.

Now other owners are claiming they have suffered similarly serious technology failures in their electric cars.

Kaur, who lives in Uxbridge, west London, said that she was taking her four-year-old son to nursery school near Gerrards Cross when she the car unilaterally engaged its driver assist (cruise control) suddenly.

She said that without her doing anything the car went from 50mph to more than 65mph, and the car’s left lane sensors started to malfunction.

“It felt like the car was wrestling against me. I tried to steer to the left to prevent the car from going on to the central grassed area. The car started to zigzag in the road. The car appeared to be in a self-drive mode and the brakes weren’t working. I had no control over it,” she said in a sworn statement to Admiral, her insurer.

Her husband, Harman Singh, who is an NHS heart specialist, added: “My wife, who had previously driven this car for many thousands of miles without incident, was so traumatised by the experience that she has refused to ride or to take our son in our other electric car.

“As a result I have had to send it back to the lease company. To me it’s a serious public safety issue – I’d be very interested to know whether any other electric BMW owners have experienced this,” he said.

A truck driver who witnessed Kaur’s crash has described how the car came down the hill “far too fast” for the road conditions, hit the grass verge, and only came to a halt after colliding with a lamp-post.

BMW challenged the claims. In a statement, it said the vehicle was travelling at 70mph, and the driver was pressing the accelerator pedal until 4.5 seconds before the 23mph impact.

This degree of deceleration could only be achieved by application of the brakes, it said.

“Our investigation established that there was no hardware or software defect and we have explained our analysis to the customer in writing,” the statement said.

“Although we regret that the outcome is not to their satisfaction, given the vehicle data, no other conclusion can be drawn. We completely refute the allegation that the vehicle accelerated of its own accord leading up to or during the time of this incident, or that the brakes failed.”

Chloe Scott-Moncrieff and Oli Jones, a couple who live in Hampshire, said they have also lost faith in their electric car. After a first year of fairly trouble-free motoring in their £52,000 Hyundai Ioniq 5, they said their car started spontaneously draining its 12-volt battery, forcing them to buy an instant charger usually carried by AA and RAC patrolmen.

“The back doors locked out of the blue for several days, then the windows. Then there were these spontaneous draining sessions of the 12 volt battery, you could never tell when this would happen, and the car wouldn’t start. This happened all over the place. In April, the car refused to move as we tried to leave the Channel tunnel and we had cars stacked up behind us,” said Scott-Moncrieff.

The final straw came when Jones found himself locked in to the car, completely unable to get out.

“It sounds funny but it was incredibly scary, not least because the charging cables were locked in the car with him. Fortunately he had his phone with him and was able to tell us where to find the spares and what to do. Had he been on his own, or away from a charger he would have had to smash the windows to get out,” Scott-Moncrieff added.

In a statement Hyundai said: “We have been unable to replicate or diagnose the issue specific to this Ioniq 5. We disconnected the battery and the doors still opened.

“The battery and a door lock have been changed as precaution. We are now in the process of sourcing a like-for-like replacement which is the preferred resolution of the customer.”