The city is already struggling with one of the highest rates of truancy in the country for children skipping school, but now the city council is turning its attention to the amount of time teachers are out of the classroom.

In 2007, 70 per cent of city teachers took at least one day off sick. This compares unfavourably to the national average of 59 per cent, while Hampshire teachers are healthier still with less than half – just 46 per cent – missing a day off school last year.

Now an occupational health team from Portsmouth City Council will visit headteachers at city schools to find out why their staff are missing so many classes.

Portsmouth City Council's assistant head of human resources, Jacqueline Coonie, said: 'When people return we've got to make sure we know what illness they had so we can make a risk assessment. We also have an advice service and we can talk to heads about specific problems.

'We want to see if there's anything that we can do to get them back in school and bring these figures down.

'Our figures are pretty much the same as all the unitary authorities. You can't compare us to Hampshire as many parts of it is leafy countryside while Portsmouth is an urban environment with people living and working close together.'

Teaching unions say teachers will not be overly worried about the extra scrutiny, as teachers absence compares well to other public sector professions.

Keith Gardiner from Portsmouth's branch of the National Union of Teachers said: 'I don't think most teachers would be concerned saying why they've been off.

'In most schools you already have a piece of paper to fill in and management is on top of things.

'In schools you have children who are alive and kicking and need to be looked after and taught all day long.

'They can't be put in an inbox or on a shelf for a week. It's a problem that has to be solved.'

Most secondary schools have a cover supervisor system where non-teachers will sit in on lessons. If the absence persists for three days a supply teacher is brought in.