© 2017 Steve Campsall
Did you find the clauses? The main clauses are shown below in red, the subordinate clauses are marked in blue (they happen, here, to be mainly relative clauses). Notice that for rhetorical effect, the writer has created a string of elliptical clauses all sharing the same subject (British teenagers) to follow the first clause:
According to a report in the British Medical Journal last week, British teenagers smoke more cigarettes, take more drugs, drink more alcohol, have more babies, terminate more pregnancies and suffer more venereal disease than those of any other European country. The thread [that connects these unpleasant facts] is the abysmally low educational and cultural level of a large section of the British population. It is not entirely a coincidence that we also have the highest illiteracy rate in Europe. We are reaping what we have sown.