Schools are forced to put youngsters through an ever-increasing quantity of exams to look good in league tables, a Birmingham head teacher has warned.

John Claughton, chief master of King Edward's School in Edgbaston, claimed the system used by the Government to rank schools was the "worst way of doing it".

It encouraged ambitious schools to "bulk buy" exams by forcing pupils to do more subjects to amass points rather than concentrating on better grades, he said.

Mr Claughton claimed students suffered as a result because the focus on points squeezed out time for extra curricular activities, such as sport.

He also maintained it damaged their chances of getting into top universities which focus more on the quality of grades candidates possess rather than the quantity. Under the current system an A-level student with four Bs is worth more than one with three As because Bs are worth 240 points and As 270 points.

It means the former is worth 960 points and the latter scores 810.

Mr Claughton said: "I do think this design of a league table where it is points per candidate which is king is a particularly distorting one because it gives credit for quantity, not quality.

"If you want to succeed in league tables you have to force kids to do more subjects.

"If you want to do well in Government tables at GCSE you do as many GCSEs as you can.

"We do ten now, but we might even want to go down to nine. We have PE lessons. We have Friday afternoon activities because we believe that is the kind of education we want to offer.

"We could offer 12 or 13 GCSEs and have lessons on Friday afternoons and no games, but we choose not to do that."

Mr Claughton said it was "absurd" that 12 B-grades beat ten A* grades.

The focus on points per candidate means grammars which put high emphasis on pupils doing lots of subjects scored more than some of the country's top independents, such as Eton and St Paul's Girl's School.

At A-levels, many schools also make pupils do general studies - a subject generally not recognised by universities - just to get their score up, added Mr Claughton.

The headteacher said his own school - where all pupils did general studies - could be used as an example of the trend, though maintained the subject was worth doing in its own right.

"If universities make you an offer of two As and a B that does not include general studies,"

he said. "But it gets between 255 and 260 points per student and completely transforms our league table performance which is why we beat Eton, Winchester College and St Paul's because they don't do general studies."

Mr Claughton insisted a much fairer way of judging exam performance was to base league tables on points per subject, which would reflect the quality of grades.

The Department for Children, Schools and Families denied league tables encouraged schools to push pupils into taking more subjects.

It said they also showed the average grade achieved in each of the qualifications a student took.