SEN appeals allow parents to challenge decisions made by authorities about their children's needs, but the cost of the system to the capital's councils alone could now be more than£1 million a year.
A survey of 15 London boroughs shows that since the Special Educational Needs Tribunal was set up in 1994, the number of appeals has leapt from an average of 22 a year to 114 in 1996.
About half of these were successful. Preparing and presenting each case costs£5,000. The 114 cases dealt with by the 15 boroughs cost an estimated£570,000.
'But what we have seen since the formation of the SEN Tribunal is giving us real concern.
'Councils are having to find up to an extra£150,000 a year from very limited resources just to meet the cost of preparing and presenting cases.'
Ms Knight accused the tribunal of making many 'inconsistent and poor quality decisions' which were costly for authorities.