GCSE results at state schools in many London boroughs have improved during the past 11 years, with huge increases in several districts where well-off parents have historically responded to poor state secondary results by educating their children privately.

Nine of the 10 English local authorities with the greatest increase in GCSE attainment since 1998 are London boroughs, according to data published on Thursday by the Department for Children, Schools and Families. The phenomenon is most pronounced in Kensington and Chelsea, one of Britain’s wealthiest local authorities, where a large minority of children forsake the state sector.