A mother was reprimanded by police after leaving her two young children sleeping in a hot car while she went shopping.

The incident occurred on Saturday morning in the car park of the Colney Fields shopping estate in London Colney, when temperatures had already soared to a scorching 23C.

Although the small children were being supervised by an 11-year-old, the situation still prompted a concerned Sainsbury’s employee to call the police.

According to eyewitnesses, when the woman returned to her vehicle, which was parked in the parent and child bays, she found it surrounded by supermarket staff, including two security guards.

One onlooker said: “A Sainsbury’s employee told her that she was putting her children’s lives in danger by leaving them in the hot vehicle, and warned her that the police had been called.

“She tried to insist that she’d done nothing wrong and only popped into the shops briefly, but he told her she had been gone for more than half an hour.

“When she said she didn’t want to wake up her children as they were sleeping he said that she was risking them never waking up if they suffocated in the heat.

“He was getting quite emotional, but that’s no bad thing, it was completely irresponsible of her to leave her kids on their own in that heat - you wouldn’t have left a dog in that car, let alone young children!”

A police spokesperson said: “Police were called to Colney Fields Shopping Park at 11.27am on Saturday. The caller was concerned about three children who had reportedly been left in a car.

“Officers attended and an older child, aged 11, was in the car with two younger children and a window had been opened. Their welfare was checked extensively and no offences were found to have been committed. However, strong words of advice were given to the parent.”

A spokesperson for Sainsbury’s confirmed there had been an incident in the store, but said they would not comment on the actions of individual members of staff.

She added: “Our colleagues are trained to report any potential risks or hazards as part of our car park safety guidelines.”

An NSPCC spokesman for the East of England said: “When left alone in a vehicle, young children can very quickly start to get anxious and distressed and there are clear added dangers when temperatures are extremely hot as has been the case this month.

“We always advise parents and carers never to leave babies, toddlers and very young children alone – whether in a vehicle or at home.”

Anyone with concerns about a child can contact the NSPCC Helpline on 0808 800 5000.