"So why are there complaints about literacy and numeracy skills on entry of school leavers into industry or university by employers and lecturers?"

That's a good question, and I think it is best expressed by the biblical observation "no man can serve two masters". Politicians have a great incentive to show their policies are working, so they like higher rates and to show everything is improving. The schools are forced by the league tables to show they are always improving and getter better results. The exam boards and so on are involved in this search for higher and higher results as well.

And all this is the exact opposite of what business wants: it wants a wide spread of grades, so only a few are 'the best' and they are easily identified. Those objectives are inherently incompatible.