The message
from Chris Hogg contains these words:

How much does wind chill effect plants? I assume that because it's a
calculated figure intended to give humans some idea of how cold it
feels, then an air temperature of say 2C with a wind chill of say -3C
doesn't actually mean plants will freeze (assuming they would anyway
at sub-zero temperatures).

Correct. With the caveat however that evaporation can be accelerated by
a dry wind passing over plant tissue or wet leaves, and this can reduce
the temperature of the plant's surface by a small amount.

But I also assume that, because of the
effect of the wind, plants will actually reach that 2C much quicker
than they would do in still air, and that their own individual
microclimate within the 'envelope' of the plant would be greatly
reduced or literally blown away.

Yes.

Which brings me on to fleece. In still air (or almost so) I assume
fleece works by preventing loss of heat by radiation

No, by convection, and thus conduction to the cool air surrounding the plants.

and thus prevents
a ground frost settling on the plant. In windy conditions, I assume
that the fleece goes some way to preserving the microclimate within
the envelope of the plant (see above) and so provides some insulation
and also prevents desiccation to some degree. Is there a rule-of-thumb
as to how much frost protection can be achieved with fleece and under
what conditions? I assume it depends to some degree on wind strength.

In windy conditions at lower altitudes there is seldom frost, though we
might be in for a drop shortly if the weather forecast is correct.

Am I right? Any views or experiences?

I've never used fleece, but if you manage to secure it and stop it
flapping about I'd guess that it would offer some protection while
frosty wind made moan.

--
Rusty
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