Complete rubbish.

You may want it to be rubbish, Martin, but it has been the regular finding of review after review over the last 30 years, at least.  The original idea of comprehensive education was to have totally mixed ability classes for every subject.  This was quickly dropped - in secondary schools at least - for all the main subjects, such as Maths, English and separate Sciences.  Today, very few secondary schools do not stream pupils according to ability in many subjects.  The only ones that are generally not streamed are Design & Technology, RE, PE and Art. Otherwise, wherever there are more than a single class's-worth of pupils taking an exam subject, you will tyend to find streaming.