Children are living in an “unprecedented toxic climate” in which they skip meals to stay thin, are bombarded by pornographic images and fear they will be failures amid a “continuous onslaught of stress at school”, according to research published today.

A poll commissioned to coincide with the launch of a national campaign found 40 per cent of 11 to 14-year-olds said they missed meals for weight-loss reasons, while a similar proportion said their relationships with other children had been affected by watching pornography online.

Half of children and young people had been bullied and more than half believed they would end up being a failure if they did not get good exam grades. The charity YoungMinds said the UK was sitting on a “mental health time bomb” and that action is needed by the Government, schools and parents to help young people cope with the pressures of modern life.

Deputy Prime Minister Nick Clegg, who is due to launch a new Mental Health Action Plan today, said the Government wanted every child who needed therapy to be able to get it by 2018.

Lucie Russell, YoungMinds’s campaigns director, said: “Every day we hear about the unprecedented toxic climate children and young people face in a 24/7 online culture where they can never switch off.

“Young people tell us they experience a continuous onslaught of stress at school, bullying, sexual pressures and bleak employment prospects. When this becomes too much for them they don’t know where to turn for help and when they do often the support just isn’t there for them. ”

The campaign, called YoungMinds Vs, aims to create “a mass movement of children and young people” to campaign for “better mental health and emotional wellbeing”, she said.

Ms Russell attacked Education Secretary Michael Gove for adding to the pressure on school children, saying the Department for Education, was “not interested in wellbeing”.

She added: “It isn’t on Gove’s agenda really. It’s all about academic success. There is a strong link between attainment and emotional wellbeing.”

She said parents “really want to do a good job” but often did not know how to deal with young people when they get stressed out.

The campaign has won cross-party support. Labour leader Ed Miliband said mental health was “the biggest unaddressed health challenge of our age, and young people’s mental health must be a top priority for Britain”.

Mr Clegg said the Government was taking action. “In Britain, one in 10 children aged between 5 and 16 have diagnosable mental-health problems. These young people often fall behind at school; they lose their confidence; maybe they don’t learn how to interact with others; and there can be knock-on effects for the rest of their lives,” he said.

“We know that there are therapies that can really help. And, working with the NHS, we’ve made them available in more and more areas. And that’s why it’s so important to me that the NHS will be extending these therapies to more children and young people. And it is Government’s ambition that, by 2018, every child in England ... will be able to access it.”

Case study: Exam pressure made teenager fear he was going to die

At the age of 15, Aiden McNulty experienced exam-related depression that got so bad he feared he was going to die.

“I was sitting my GCSEs and I was getting a lot of pressure from family members and teachers and I was putting a lot of pressure on myself,” he said.

“I was thinking, ‘Crikey, if I fail, I’m not going to be able to go to sixth form or university.’ I started getting headaches and nosebleeds and I convinced myself I was getting really ill. I was locking myself away, feeling the pressure. I was depressed as well, it was just a general bad time. I convinced myself I had a brain tumour. If you are diagnosed late, you’ve only got about three months [to live].”

The feelings lasted for about six months and he performed badly at school, getting D and E grades. However, the teenager, from Wallington in south London, eventually sought help from his family and his GP. He realised he was not dying and many of the feelings he was experiencing were normal.

His exam results improved dramatically and he is now in sixth form with several offers from universities to study business management.

He urged anyone in a similar situation to seek help, saying had he not done so he “probably would have ended up on anti-depressants”.