Almost a quarter of UK A-level entries were awarded the top grade this year.
The proportion of exam entries that achieved an A was 24.1%, up 1.3 percentage points on last year, said the Joint Council for Qualifications.
Amid continuing concern, ministers are making changes to stretch the brightest students and help universities distinguish between the top performers.
The overall A-level pass rate rose for the 24th year, by 0.4 to 96.6%. There were markedly more entries for maths.
There was a record number of entries overall at 805,698, 2.8% more than last year.
Girls outperformed boys in every major subject apart from modern foreign languages, according to the joint council (JCQ), which is the umbrella body for the main exam boards in England, Wales and Northern Ireland.
'Day of celebration'
JCQ director Ellie Johnson Searle said: "The hard work of students and teachers is clear, especially when judged against the continuing rigour and robustness of the assessment system in the UK.
A-LEVEL RESULTS
"The turnaround in mathematics - both in overall numbers and in achievement - is encouraging in the first year of the new specifications."
"Hard work merits success "
But he has conceded that, as more students get top grades, universities find it harder to distinguish between them.
From next year, universities will see the grades for each of the six units that make up an A-level, as well as the overall result.
To provide more challenge, students are likely to be asked to produce an extended project, and to face tougher questions in their A-level papers - with perhaps an A* grade, as at GCSE level, to identify the brightest.
But John Dunford, general secretary of the Association of School and College Leaders, said adding an extra grade at the top would "increase stress and anorexia in 16 to 18-year-olds".
NI students did best
As usual, the Northern Ireland entries were the most successful this year, with a pass rate of 97.7% and almost a third - 32.4% - awarded A grades.
In Wales, 96.9% passed with 23.9% getting an A.
SUBJECT ENTRIES
England did worst, relatively: 96.5% of entries passed and 23.8% achieved an A.
Too few students in Scotland take A-levels for the figures to be published separately.
Also published were the results at AS-level, the halfway stage towards a full A-level and a qualification in its own right.
The overall pass rate rose 0.2 to 87.5% and 18.4% were awarded A grades (up 0.5).
The difference between the AS an A-level success rates reflects how students tend to drop their weaker subjects as they go on to complete their two years of study.
Of the 632 students who completed the Welsh Bac - still being piloted - 87% achieved the Core Certificate and 76.4% were awarded the full Advanced Diploma.
League tables
Although candidates get their individual results on Thursday, the national figures relate to exam entries rather than individual students.
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Provisional national statistics on how the students have performed, such as the proportion getting two or more A-levels and their average points scores, will not be available until October.
The national school and college "league tables" for England, based on the results, are not published until the New Year.
GCSE results are due to be published next week - on Tuesday for the Northern Ireland exam board, and on Thursday for the others.
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