Overall UK GCSE pass rates have fallen this year amid the biggest shake-up of exams in a generation.
Around 18,600 students scored a 9 in maths - the new highest grade - while almost 31,000 achieved the top mark in the two English GCSEs combined.
Under the overhaul, traditional A* to G grades are being gradually replaced in England with a 9 to 1 system.
English and maths - key GCSEs for all teenagers - are the first to move across, with other subjects following over the next two years.
Today's figures show that across England, Wales and Northern Ireland, the proportion of entries scoring at least an A grade - or a 7 under the new system - has fallen by 0.5 percentage points to 20 per cent compared to last summer, while the percentage gaining a C or above - or a 4 under the new system - is down 0.6 percentage points to 66.3 per cent.
The statistics, published by the Joint Council for Qualifications (JCQ), show that among 16-year-olds in England, girls outperformed boys in achieving grade 9s in both English GCSEs, while boys did better in maths.
Fewer candidates have achieved a 9 compared to the proportion that gained an A* under the traditional A*-G grading system, following the deliberate move to change the system to allow more differentiation, particularly between the brightest candidates.
The grading switch is part of wider reforms designed to make GCSEs more rigorous and challenging.
There are now three top grades - 7, 8 and 9 - compared to two under the old system - A* and A - with A* results now split into 8s and 9s.