What is the difference between Competence, and Competency?

The idea of 'competencies' vs 'competences' took hold in 1980s (Management Today Apr 2010 p69): a core COMPETENCY is a particular attribute required by someone's job, such as IT skills, industry know-how, or customer service (the output)
whereas a COMPETENCE (defined by Chartered Institute of Personnel Development) is the minimum standard demonstrated by performance outputs, rather than individual traits.
HR departments measure both, in particular to determine how well an individual meets the requirements of their job (how far the competences go towards fulfilling the competencies), and of course identifying candidates for promotion. Perhaps the easiest way to look at it is a Competency is what is required for the job, and a competence is what you have.
The problem is that such paper competence offers little insurance against real-world incompetence. All of us probably know someone who performs well on paper, shines at interview, yet appears hopelessly incompetent in the real world. Sir Alan Sugar hit the nail on the head when he described one of the front runners as "will do extremely well in a corporate environment and rise through the ranks, but i want people who can create a profit"
Promoted to the level of their incompetence! How common is this? Actually, it's quite a natural process. Someone who has been competent in a role often finds themselves promoted. There will come a point, unless they are conscious, continuous learners, where they will end up in a role for which they aren't competent, and labour laws and the way management work mean that once promoted someone can't be demoted again.
Perhaps the answer is to promote anyone and everyone "for a trial period" (of say, 12 months) and then re-appraise. But this needs to apply at all levels even executive board level and Chief Executive, and it needs to be an accepted part of the culture and enshrined in labour law before we can do it.
What do you think?