The number of Sussex pupils in the worst category of school truants is set to rocket as part of a government crackdownon skivers.

Ministers have unveiled plans to widen the net and place thousands more youngsters in the “persistent absentee” bracket, forcing schools to take action sooner.

This would single out almost 12,500 Sussex youngsters for action.

The move was criticised by teaching unions, who said the “arbitrary targets” would have no real effect.

Schools Minister Nick Gibb, MP for Bognor Regis and Littlehampton, announced the definition of persistent absence used in the school performance league tables would be cut from 20% to 15% to deal with the “reality” of pupils skipping school, and the impact it has on learning.

The Government believes tightening the criteria from October to include those who miss 15% of their classes – the equivalent of a month’s schooling each year – will mean a national increase from 184,000 to 430,000.

Latest figures show there are 5,342 children currently classed as persistent absentees (PAs) across Brighton and Hove, East Sussex and West Sussex, a figure which would rise to about 12,484 according to the new criteria.

As things stand, 3.4% of pupils in Brighton and Hove are classed as persistent absentees, compared to 3.2% in East Sussex, 2.8% in West Sussex, and a national average of 2.9%.

Experts say there is clear evidence of a link between poor attendance at school and low levels of achievement.

Of pupils who miss between 10% and 20% of school, only 35% manage to achieve five A* to C GCSEs including English and maths.

Brighton and Hove City Council leader Bill Randall said: “Recognising the clear link between poor attendance at school and low levels of achievement, we have worked hard to reduce the number of children persistently staying away from school.

“As a result, persistent absence went down in the city from 8.3% in 2005/06 to 5.9% in 2009/10. The Government’s decision to change the definition of PA from 20% to 15% will give added impetus to early intervention where a pupil is not attending school regularly.”