Many of the country's top private schools will find themselves at the bottom of the league tables today following a shake up of the GCSE system.

It comes after the government announced International GCSEs (IGCSEs) - used by many private schools as they are deemed more rigorous - would no longer be counted in the rankings.

Figures out today reveal the number of secondary schools considered to be under-performing has also doubled in the wake of the overhaul of the exams system.

But school leaders have branded the move to drop IGCSEs from the rankings as "nonsense".

School leaders are launching alternative league tables to 'accurately' reflect their results. Credit: PA

Richard Harman, chair of the Headmasters' and Headmistresses' Conference (HMC) 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.

"This obviously absurd situation creates further confusion for parents as they cannot compare schools' performance accurately and transparently.

"Many HMC schools will continue to offer the IGCSE as experience tells us it is rigorous and offers a good basis for sixth form study."

The new league tables, based on Department for Education data, show how every school and college in England performed at GCSE, A-level and other academic and vocational qualifications in 2014.

State secondaries are considered to be below the Government's target if fewer than 40% of their pupils gain at least five C grades at GCSE, including English and maths, and students are not making good enough progress in these two core subjects.

In total, 330 schools fell below the benchmark this year, up from 154 last year.

Schools that fall below the threshold could face action, including being closed down and turned into an academy, or being taken over by a new sponsor.

Education Secretary Nicky Morgan said the Government has "raised the bar" and that schools were already rising to the challenge.

She added: "For too long pupils were offered courses of no value to them and schools felt pressured to enter young people for exams before they were ready.

"By stripping out thousands of poor quality qualifications and removing results from tables, some schools have seen changes in their standings."

Almost 90,000 students are now taking core subjects than four years ago. Credit: PA

This year's top school for GCSEs was King Edward VI Five Ways School, an academy in Birmingham.

It entered 155 pupils for GCSEs and equivalent qualifications and all scored at least five C grades, including English and maths. It also had the highest average points score per pupil at 685.5.

The most improved school was the Charter Academy in Southsea which has seen its results jump from 39% of students getting at least five Cs including the basics in 2011 to 83% achieving this standard in 2014.

Figures show 90,000 more teenagers are now taking more core academic subjects and 50,000 more are taking a language than four years ago.

While the number of pupils entering for the English Baccalaureate (EBacc) has risen by 71%.

The top schools for the EBacc this year were Altrincham Grammar School for Girls and Queen Elizabeth's School in Barnet, where 99% of pupils who entered the EBacc achieved it.

The Association of School and College Leaders (ASCL) has launched an alternative league table after saying the government model "does not give a full picture".

ASCL general secretary Brian Lightman said: "We want parents to have as much information as possible, but it needs to be presented in a way that is genuinely useful and gives a clear, a full picture of the quality of education that schools provide and the outcomes that young people achieve. That is what really matters.”