I've just had a reply from the Wavin (Hep2O) Technical Design Department; "we have no issues with our Hep2o system being clipped over the insulation and this is a principle we see on site often.
However, we would not recommend builders band is used, we would recommend that suitable pipe clips are used i.e. rubber lined, Talon clips etc."
So it seems that it would be fine. When the time comes, I'll either find clips that will work or maybe take a look at designing something for 3D printing and then print them in red and blue filaments...
Thanks for the input @Super_Paulie and @joth - much appreciated.