A possible remedy would be the introduction of a preliminary communication test (PCT).
This would cover the simple skills which the employers say are lacking. This test would be taken early during the last school year, with one re-sit if necessary. It would be monitored by a committee of employers and teachers. To ensure that this idea is taken seriously, no candidate for GCSE would be allowed to proceed without a pass in PCT.
The standard of PCT would be such that "more able" pupils would be able to pass provided that they took a little trouble with the basics.
In addition most of the "least able" could be awarded some sort of PCT certificate, to improve their morale and indeed their employment prospects.
As a final bonus, judging from comments by university teachers, it is just possible that it would be revealing to give a preliminary communication test to undergraduates in their final year.
Emeritus professor of mathematics education University of London