Now I see where I have been getting it wrong all this time. There I was thinking that if I was cleared on an ILS approach (not a practice ILS approach) to a radar equipped airport that all I should have to do was concentrate on my scan till DH regardless of what the weather was doing outside of the window and I would be protected....clear skies and a quick lookout just being a bonus.
Yup. You've been getting it wrong.
Would any of the "see and avoid" advocates in this case like to extend their argument to explain how a large commercial aircraft with a fairly swift approach speed (say Concorde or an A380) is supposed to see and avoid a microlight in those conditions ?
Easy. Choose not to operate into airports which involve flying the approach in uncontrolled airspace.
Surely the approach is either protected or it isn't ?
Correct. And you can tell the difference by looking at the chart, which will tell you whether the approach is in controlled airspace (protected) or not (not).