Since 1990 there has been a dramatic fall from 45,277 A-level entrants in 1990 to 32,801 in 1996, despite a massive rise in the number of A-levels taken overall.
Jonathan Ling, director of studies in the physical sciences at the University of Hertfordshire, says the subject is being reduced to a hard core of the most able students.
Despite the diminishing number of physics entries, the total getting grades A-C has remained surprisingly constant at around 20,000, says Mr Ling. The number of lower grades has dropped.
"There's a feeling that physics as a whole is something people aren't tackling," said Mr Ling, honorary secretary of the ASE. "Because of its difficulty people are turning away from physics towards subjects like psychology and business studies."
Research produced in 1994 suggested that maths and physics are, on average, one grade more difficult than other, non-scientific subjects. In the light of this, Sir Ron Dearing's review of 16-19 education recommended that the examining boards should examine the comparative difficulty of A-levels to ensure there are no soft options.
A-level physics is particularly unusual in that it is the only school subject in which girls' performance is getting worse. Girls now outstrip boys in most subjects at GCSE, and at A-level they are catching up. But in physics the gender gap is growing. Since 1988 the ratio of boys to girls taking physics A-level has increased from 3.41:1 to 3.54:1.
The decline in numbers taking physics is associated with a parallel decline in the numbers taking mathematical mechanics, an allied area of study. Mr Ling believes this could be because neither physics nor mechanics are now seen as subjects which would be useful in students' later educational careers. Some degree courses which once demanded a subsidiary study of physics have dropped it, he says.
In contrast statistics, which is seen to have widespread application across a range of degree courses, has shot up in popularity.