I've just been contemplating a tap-replacement project, and considered
(ok, I've just bought) flexible tap pipes - the type with braided hose
and a compression fitting at one end. The obvious problem is how to use
the compression fitting on the existing plastic piping?, a quick google
suggests that you need an insert for the pipe (I can imagine a copper
sleeve with a slight rim, that is inserted into the end of the cut
plastic pipe - to avoid undue distortion to the plastic pipe when the
olive bites).

Is this the right track (in which case, I really, really should have
included these in the old screwfix order) - can these be *readily*
picked up (i.e. in the Sunday sheds, rather than plumbers merchants (who
all seem to close at the convenient times for most people in full-time
employment)

Regards

Mike