I thought it might be handy if anyone needed to know how to remove the grille inserts to gain access for routing wiring or aerial cables, although it's pretty straightforward...
1. Remove the two black expanding clips from the top of the grille insert (circled in red). Just prise out slightly the centre plug of this clip to release it, and pull each one out.
2. With your finger or an angled tool (like an allen-key head) pull upwards on the 4 inside tabs to release them from the slots in the bumper section (circled in yellow)
3. Gently pull outwards and upwards to remove the insert - in the bottom corner near the headlight is a final clip that slides from a slot on the insert. Be careful not to angle the grille insert too far or this might break (circled in purple)
4. Hopefully you're done!!
Both sides are removed the same way. To put it back on is basically a reverse of the above, taking care not to force any of the tabs or the slot when you're doing it.
Cheers!