The government has targets for more physics teachers by 2014
Almost one in four secondary schools in England no longer has any specialist physics teachers, a survey suggests.
The report into the supply of physics teachers, published by academics at the University of Buckingham, warns of a threat to the subject's future.
The government has set targets to promote the number of physics teachers in secondary schools.
But the report's authors warn that half of the schools in inner London do not have specialist physics teachers.
The report, by Professor Alan Smithers and Dr Pamela Robinson of the Centre for Education and Employment Research, says that 26% more physics teachers are leaving or retiring than are being recruited.
From September, pupils who do sufficiently well in tests for 14-year-olds will have an entitlement to be taught physics. But this report highlights concerns that this will have to be provided by non-specialist staff.
The survey shows substantial differences in the availability of physics teachers - both regional differences and by the type of school. And it raises concerns about the viability of physics as a separate subject.
In inner London, there is a tendency to have general science teachers rather than specialist physics teachers - and 50% of secondary schools do not have any physics teachers.
In contrast, in the Yorkshire and Humberside region, only about 10% of schools do not have any specialist physics teachers.
Where schools have sixth forms, they are much more likely to have specialist physics teachers. However in schools without sixth forms, about two in five schools do not have any specialist physics teachers. Instead they will have teachers from other disciplines who will take combined science classes.
The research also shows that physics teachers are more likely to be concentrated in particular types of school, such as those which are high-performing, grammar, all-girl and faith schools.
The report's authors argue that physics has been pushed into decline by a drive for general science courses. They call for the subject to be supported in a way that protects its separate identity.
"One admissions tutor said: 'Until recently we have barely admitted that physics existed as a school subject - physics, chemistry and biology have not been allowed to be mentioned in official documentation'," says the report.
The government wants to promote science subjects such as physics and chemistry and has a target that 25% of science teachers in England will have a physics specialism by 2014.
A spokesperson for the Training and Development Agency for Schools said: "We have helped secure a significant increase in the recruitment of physic teachers, up by almost a third last year and the previous year. The number of science teachers overall hit 3,000 for the first time ever last year.
"We are investing £7m in enhancement courses for teachers with related degrees to become physics teachers. This produces up to 150 new physics teachers a year.
"Both the Institute of Physics and Ofsted confirm that these courses are succeeding in producing good physics teachers."
A spokesman for England's Department for Children, Schools and Families said it was investing £140m over the next three years to enhance recruitment and retention of physics and chemistry specialists and to help boost the number of young people studying science subjects post-16.
"The number of pupils taking individual physics, chemistry, and biology GCSE is rising and by September 2008, all pupils achieving at least level 6 at Key Stage 3 will be entitled to study triple science GCSE," he said.
Primary school teaching
Other efforts included after-school science clubs and 18,000 "science ambassadors" - people with industry experience in science and engineering who would enthuse young scientists.
Meanwhile Scotland's science centres are to get an extra £250,000 this year in an effort to improve primary school teachers' delivery of science subjects.
Last month the annual Scottish survey of achievement in science showed that too few pupils were achieving the expected levels in science.
Scotland's education and lifelong learning secretary, Fiona Hyslop, said: "Scotland's economic future is increasingly dependent on science, engineering and technology."
She added: "Our children must be inspired by the world of science and, in order for that to happen, they need the best teaching available."