Far fewer Croydon students hit the top grades in last year's GCSE exams, official league tables showed today.

But the results have been branded "nonsense" by private schools because of a controversial change in which qualifications are recognised by the Department for Education.

Across the borough 56.8 per cent of students achieved the Government benchmark of five A* to C grades in last years GCSEs, down from 64.4 per cent in 2013 and the lowest proportion for several years.

But some of Croydon's top-performing independent schools, including Whitgift, Trinity and Croydon High, were officially recorded as having no pupils hitting the top grades following confusion of unaccredited exams.

The Government this year phased out international GCSEs, favoured by many private schools as more rigorous, from its performance data.

Richard Harman, chairman of the Headmasters' and Headmistresses' Conference , which represents many leading independent schools, said omission made the tables "absurd".

He said: "Several of the UK's most highly performing independent schools and others offering this excellent qualification will now appear to be bottom of the class in the Government's rankings."

Last year Trinity School, in Shirley, was joint-highest performing in Croydon with 100 per cent of students achieving five A* to C grades.

Addiscombe's Al-Khair School tops this year's table 100 per cent of pupils achieving five A* to C grades for the third consecutive year. 

Coloma Convent Girls' School, Croydon's second-highest performing school and the borough's top state-funded, saw its A*-C pass rate drop from 95 per cent to 90 per cent. 

Of the schools sitting traditional GCSEs, Addington High School recorded the worst A* to C pass rate, with 37 per cent of students achieving five top grades in its first year since becoming an academy.

A-level league tables were also published today, with Croydon students' grades rising from last year. 

The borough's post-16 students scored 205.4 university application points on average, up from 199.9. 

Trinity School boasted the highest average of 255.9, while Croydon College recorded the lowest of 156.5.