Sir Peter Williams, who was appointed last week to review the teaching of maths in primary schools, said that the A-level gold standard had been slipping for a 'long period of time'.

The distinguished academic and businessman, who chairs the Advisory Committee on Mathematics Education (ACME), said: 'Over 20 or 30 years, I don't think there is any doubt whatsoever that absolute A-level standards have fallen. They have edged south, continuously over a long period of time. I think all university academics and a good proportion of sixth-form teachers would agree with my assertion.'

The idea that A-levels are getting easier is a widely held perception, he added, but in his own areas of physics and maths it is also a 'testable fact'. He said that he did not, however, think the decline 'disastrous'.

Looking at maths exam papers, Williams, who is Chancellor of Leicester University, found that A-level students faced equations today that required less depth of knowledge and understanding than in the past. As a result, universities had been forced to adapt, he argued. Some three-year courses were now stretched over four, while in physics, for example, thermodynamics was being taught in the second year rather than the first because students needed a year following simpler studies.

Williams is a leading figure in the education world, having held a string of illustrious positions. He is currently chair of the internationally respected National Physical Laboratory and has also been a Master of St Catherine's College, Oxford, and president of the Institute of Physics. His comments are significant because the Government has always maintained that improving exam results are due to better teaching and pupil effort rather than dumbing down. 'There is a general misconception that the A-level has become impossible to fail and that A grades are handed out like sweets. This, like many myths surrounding the exams, is nonsense', then Schools Minister Jim Knight said last year. In 2005 the Headmasters' and Headmistresses' Conference, which represents more than 200 independent schools, said it was considering dropping A-levels altogether.

A study carried out at the CEM centre, an education research unit at Durham University, has recently suggested a dramatic decline in maths standards. For nearly two decades up to 50,000 pupils a year have taken the same ability test before facing A-levels. Researchers found that, in most subjects, pupils of the same ability achieved two grades higher in their A-levels in 2006 than in 1988 jumping to three grades in maths.

In recent years senior figures in universities and in business have complained that they are struggling to differentiate between the good students and the very best.

Williams said that A-levels needed 'fine tuning' with optional, tougher questions, rather than being completely changed. He welcomed last week's announcement that A-level students achieving more than 90 per cent would be rewarded with the new 'A-star' super-grade, and there would be 'Oxbridge style' questions added to exams.

He also commended the Further Maths Network for successfully persuading more of the brightest pupils to take higher-level maths exams.

'I believe that, with some more stretch and challenge inserted into it, the A-level is still the right vehicle,' said Williams. 'We should not decry the fact that increasingly large cohorts of young 18-year-old men and women attain higher levels in their graduation qualification coming out of secondary education. That is something we should applaud. It is the universities' job, then, to somehow select the most appropriate pupils.'

Robert Coe, director of secondary projects at the CEM centre, said one of the things driving down standards was competition between exam boards.

'I agree with everything Peter Williams is saying,' he said. 'With a slight rider - is this a bad thing? Yes, A-levels have got easier, but for the majority of people who take them that means they are better suited to the type of performance they are going to achieve.'

Speaking about mathematics in particular, Ken Boston, chief executive of the Qualifications and Curriculum Authority, said there would be extra 'stretch' to help pick out the best performing students and 'strengthen the A-level'.

Ministers were accused of 'dumbing down' GCSEs last week after it emerged that up to half of the marks in GCSE English would be awarded for skills as basic as punctuation. Pupils will also face multiple choice questions as part of the exam.