Ministers are overestimating the number of exceptionally bright pupils in Britain's schools, the World Council for Gifted and Talented Children will be told this week.

Research shows that teachers charged with picking out the top pupils feel that far too many are labelled as 'gifted and talented' and that the government was wrong to recommend that 10 per cent were picked out in each school, a total of 800,000 across the country. Instead, between 2 and 5 per cent of children should be classed as 'gifted learners', cutting hundreds of thousands of pupils already placed in the top group.

'Teachers said they felt they had to control the number of children in their classroom who are gifted and talented,' said Dr Thomas Balchin, an academic at Brunel University, who carried out the research with 800 co-ordinators. 'Unfortunately, in many schools, typically the inner-city schools in disadvantaged areas, co-ordinators are convinced they really only have 2 to 4 per cent.'

He added that in some schools, nearer 30 per cent of pupils should be classified as exceptionally able under the same criteria, but many teachers felt under pressure to stick to the 10 per cent recommended by ministers.

While the government asks schools to identify just 5 per cent nationally of the top pupils aged 11 to 19 for membership of a student academy for the gifted, it also asks them to pick out 10 per cent of pupils in each school as 'gifted and talented'. In Wales and Scotland teachers go further, choosing 20 per cent.

Balchin's work also looked at problems in the type of children being identified. Many teachers felt that bright children who were bored in class, misbehaved or did not flourish in traditional lessons were being missed out, despite being extremely gifted. Others who behaved well and handed work in on time were far more likely to be chosen as talented.

The research will be presented to the council at its annual conference which opens today at Warwick university, the government's centre for the promotion of the country's bright children, attended by academics from more than 50 countries .

Many will disagree with Balchin's call to cut down the numbers classified as gifted and talented. 'Why only identify 2 to 5 per cent?' said Johanna Raffan, chair of the programme committee for the conference. 'Ten per cent may seem a blunt measure, but by being told to identify 10 per cent, schools have to address this issue.'

Professor Deborah Eyre, director of the government's Academy for Gifted and Talented Youth, said: 'Wherever one draws the dividing line is entirely artificial. The only reason is a resource issue - if you are going to target additional resources, you need to draw a line at where the resources are available.'

But others argued that there were not the resources to meet the needs of 10 per cent. 'I am a passionate supporter of the gifted and talented,' said Sir Cyril Taylor, a leading government adviser. 'But if you are doubling the numbers, where is the budget? Are you trying to get schools to spend their own money?'

Taylor argued that providing extra support must be accountable, so pupils who are identified should be expected to get three As at A-level, which is not a realistic goal for 10 per cent of pupils in each school.

Other experts recommended a different approach. Professor Joan Freeman, a psychologist working with able children, said that pupils should be able to voluntarily sign up for extra classes.

Meanwhile, Belle Wallace, a consultant on gifted education, will present research on a study she has been carrying out with schools that not only identified 10 per cent of pupils as gifted and talented, but also highlighted a 'shadow group' who could move into the top category at any time. 'We have to keep an open-door policy because intelligence and talent are not fixed,' she said.