Prior to 1974, although the teaching of the metric system was not compulsory, many schools did in fact teach it, and it was included in some examination syllabuses. However, since 1974 all state schools have been required to teach the metric system as the primary system of measurement. The National Curriculum now requires only a familiarity with the names of old imperial units and, more recently (because of some unfortunate backsliding on metrication), approximate conversion factors for imperial units deemed still in common use.
Unfortunately, although the emphasis within the mathematics and science curriculum is on metric units, there is no requirement for teachers to use or encourage the use of metric units in other subjects such as geography or on the sports field. Children therefore learn that imperial units are "normal", whereas metric units are for science and maths. UKMA believes that teachers should be expected to use exclusively metric units throughout the school's activities. In this way, the learning in the science and maths lessons will be reinforced rather than undermined.
Meanwhile, even older people (say, born before about 1960) who learnt only imperial at school have had ample time and opportunity to become familiar with metric units - and many have done so without difficulty.
So spare a thought for young (and not-so-young) people who only really know the metric system who have to muddle through a confusing world of dual measures. Could there be a connection with the UK's reported numeracy difficulties compared with other nations? Because of the UK's failure to implement the change to metric in a timely or comprehensive manner, nearly two generations have passed through the school system having being taught the power and simplicity of the metric system only to be discouraged from applying it fully in everyday life.
See also the views of John Muir, an educational adviser.