The warning has come from academics at the University of East Anglia (UEA), who found that 51 per cent of British children aged seven to 11 cannot swim the distance.
The curriculum requires that children should be capable of at least that length by the time they arrive at secondary school.
The academics say that, because of this failure, secondary school PE teachers are having to pick up the gauntlet.
Dr Craig Avieson and Dr Penny Lamb, of UEA’s School of Education and Lifelong Learning, set out the problem in an article in the journal Physical Education Matters.
Dr Avieson said: “It is a national problem that children cannot swim by age 11. Ensuring children have basic swimming skills is the responsibility of both primary and secondary schools and this is a chance to do something about it.
“Teaching children such an important life-skill should be a priority and there should be joined-up thinking between primary and secondary schools to address this issue.”
Reasons behind the decline include a lack of funding, cost of transport and limited access to swimming pools, particularly in rural areas.
Dr Avieson and Dr Lamb have now presented a new model for schools using the Amateur Swimming Association’s (ASA) National Curriculum Training Programme to prepare trainee teachers to give swimming instruction.
It has been developed through a pilot study with UEA’s secondary PGCE PE programme and gives trainee teachers confidence in teaching swimming and ways to support lower-ability children.
Susan Barlow, manager of the ASA’s School Swimming programme, said: “With 51 per cent of primary school children unable to swim the minimum of 25 metres, it has become essential for secondary PE teachers to understand the fundamental, core aquatic skills of swimming and how these skills transfer to the development of swimming strokes and other aquatic activities.
“The programme allows secondary PE teachers to gain this knowledge and understand where these key skills fit.”
She added: “The number one resource is school teachers: with the correct training they can give pupils the best possible start to swimming.”
The ASA has recently created a website for teachers providing guidance and support.
For details, visit www.swimming.org/schoolswimming