The health and education of children living close to airports is being severely damaged by the noise of aircraft. The findings, detailed in a new Department of Health study, will put pressure on the Government to reject controversial plans for a fifth terminal at Heathrow Airport.

The report, which was completed last November, has still to be made public. But The Independent on Sunday has learnt that the study says aircraft noise damages children's health and education prospects. The study, by a team of psychologists at London University, is the most comprehensive yet into the effect of chronic noise. It was commissioned by the Department of Health in the wake of the Terminal Five planning inquiry, the longest and most expensive ever.

The decision on whether to build the £2bn terminal is expected in the summer. The terminal would open in 2007 and hugely increase the number of flights to the airport. Currently 453,000 planes a year take off and land at Heathrow.

The noise study will provide powerful ammunition for campaigners protesting against Terminal Five but they have so far not been allowed to see it. It confirms the findings of similar reports carried out in Sweden, Germany and the US. One report showed the reading ability of children aged 12 to 14 was "23 per cent impaired" when affected by aircraft noise. Another study showed children exposed to aircraft noise were much more likely to develop anxiety disorders.

It is understood that on the day the Heathrow study is finally published, children who took part in it, and their parents, will each receive a letter explaining the report's findings and the possible consequences the terminal may have for their education and well-being.

One protest group, with 25,000 members, accused the Government of suppressing the report until after the Terminal Five announcement is made. "We are appalled at the fact the Department of the Environment is holding back this vital piece of research," said John Stewart, chair of the Heathrow Association for the Control of Aircraft Noise. "It should be put into the public arena before the decision on Terminal Five is made."

The London Borough of Hounslow, which opposes Terminal Five, also called for the immediate publication of the report.

"The West London Schools Study", by psychologists at Queen Mary and Westfield College, follows a smaller study by the same team commissioned by the borough. That suggested that chronic aircraft noise exposure was associated with impaired reading comprehension and high levels of noise annoyance but not mental health problems in children.

Aircraft flying over schools near Heathrow has long been a problem in the classroom. School buildings in the borough of Hounslow cost on average 15 per cent more than elsewhere in London because of the cost of sound-proofing measures such as double-glazing. That makes schools hot, so the council then has to pay to install air-conditioning in classrooms.

Mary Otway, deputy headteacher at Springwell Infant and Nursery School, which is about two miles from Heathrow, said lessons were often interrupted by aircraft. She added: "If you are teaching in one of the huts near the playground you just have to stop talking when a plane flies overhead. That happens about every minute in the height of summer.

"When the planes are taking off over the school that is worse. The whole school is affected then. It is distracting for the children and it is distracting for the staff. I know some teachers whose voices have suffered from having to speak so loudly. So what it is doing to children's hearing, who knows?"

Jon Phillips, spokesman for British Airports Authority, which wants to build Terminal Five, said: "I am not aware of the new research. All I can say is research presented at the planning inquiry failed to detect a significant effect [on children's health and education].

"It is not BAA which decides where to build a school and it is not BAA which decides what degree of building standards a school should have."