On the contrary, Sandra and Doug, from Stanwell in Middlesex, are attentive parents who regularly read to their children, play with them and take them for walks.

“Sometimes it would take us an hour just to get them out of the house and into the car,” says Sandra, who works in admin.

"They’d hit us in the face or throw themselves on the ground.

"It was as if they had all the power and they knew there was nothing we could do about it."

Until recently, family support worker Ruth Gort ran Tulip, a group for parents like Doug and Sandra, the only one of its kind in the country.

“I’d estimate there are at least 10,000 parents in the UK being physically bullied or beaten by their own children,” says Ruth.

“It’s becoming a national crisis.

"Sadly, we had to wind up Tulip because social services were referring so many cases to us that we didn’t have the manpower or funding to answer the phones.

“One desperate mother rang to say her teenage son had kicked her repeatedly in the stomach.

"She was pregnant by her new husband and her son wanted to get rid of the baby.”

Sandra Douglas is now convinced her twins’ problems might have had something to do with lack of discipline.

She and her husband do not believe in smacking.

Sandra adds: “Looking back, I think we might not have imposed clear enough boundaries in the early days.”

But Sandra and her family are at last finding a way out of their crisis.

“We realised that we had to be the ones in charge,” says Doug, a customer services agent.

So they’ve now imposed stricter rules and also changed the twins’ diet, cutting out the sweets and fizzy drinks that could make them hyperactive.

“We’ve also learned that physical exercise makes them calmer, so they're running around more now and things are slowly getting better,” adds Doug.

Mary*, 52, from Hull, has spent years trying to work out where she went wrong with her son Michael, now 21.

“It started with him just nudging me when he was about 10,” she recalls.

“He realised that I gave in if he pushed me. I was too ashamed to tell even my husband, so I hid the bruises.”

But one day when Michael was 13, he locked Mary in his bedroom with him, hid the key, then put his boots on to give her what he called “a well-deserved kicking for not being a good enough mother”.

Two weeks later Michael attacked Mary again.

This time her husband Sam was in the house and tried to intervene, falling victim to a beating from his son in the process.

“I’ve spent years trying to work out if it was something we did.

"The only reason I can come up with is that, because he was an only child, we overindulged him and allowed him to walk all over us.”

Mary finally called the police when her son was 15.

“I realised he could kill me. He was 6ft tall and he’d thrown a chair at me.

"He was taken into care and now he’s living with his girlfriend. I still see him but his dad won’t.

"I can’t cut that tie. I still love him.”

Michelle, 49, a single mum from Surrey, is also struggling to come to terms with her child’s violence.

She works as a school secretary, and her 12-year-old son Jake is living with a foster family.

“As a toddler he became very aggressive. Even at two, he was strong and could really hurt me,” she says.

“He was eight when he attacked me with a kitchen knife because he couldn’t find his favourite jeans.

"I rang 999. I was at my wits’ end, terrified for my life.

“The police arrived, and it was decided that he should go into foster care.

"As they drove him away, I broke down.

"He could be such a loving boy – he’d cuddle me and say: ‘I love you, Mum.’ I felt I’d failed him.”

Michelle now sees Jake once a week for two hours, in the presence of social services.

“Every time I see him I think I should have him back home,” she says.

“In his round glasses he looks just like Harry Potter, as if butter wouldn’t melt.

"But I know the violence would start up again and he could kill me, so I have to harden my heart.”

Have you run into difficulties with your children? How do you think it's best to control unruly kids? Do you believe in smacking? Do you think that children's behaviour is the fault of the parents?

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Photography: Karen Hatch, Getty Images; Hair and make-up/styling: Kellie Mitchell; Photograph posed by model

* All names have been changed