So nearly 10 years on, I've followed this guide and found it excellent. I just thought I'd add a few more points for what I imagine is now a very small number of people who will be attempting this.
I have a 2015 QV and bought the Oris (Bosal) detachable towbar from PF Jones as well as the universal wiring kit.
The 3 screws holding in the fabric-y wheel arch onto the bumper had totally seized. I used an angle grinder to get these out. I replaced the spire clips and they have done a job.
Absolutely try and get the rear lights off for removing the bumper. I used a plastic picnic knife that I sanded down and worked a treat.
For drilling holes in the bottom box sections, I used a step drill bit. The nature of the QV's dual exhaust means that you need an extension bit to drill the rear holes. The step bit I used was £12.99 from Screwfix and totally wore out by the end because the steel is so tough.
For the Bosal towbar at least, whilst the minimum size of hole to drill is about 13mm for the bolt, the 18mm recommended hole is to cover the total lack of precision that the towbar is manufactured with. But that's okay because it's absolutely solid once installed.
I found that the bumper cut needed to be another centimeter wider on the left hand side to allow the swinging-down electric socket to freely swing.
I had a fat red power cable heading to the rear fuse box as described, probably because I have the heated seats. It was an absolute pain in the arse to fit into the clip, but a lot of electrical tape sorted that.
The blue clips described in this guide were red for me.
If I think of more points I'll add to this, and some photos if people need.
Step drill for sure, although my eBay special step drill bit is still fine after doing the chassis leg holes on the alfa, on my mate's i30 wagon and a bunch of other random jobs.
Agreed on the hole size, i would stop at a smaller size doing it again - my Autohak bar lined up perfectly in all regards. Can totally recommend the Polish tow bar makers. I fitted a Bosal to my last Clio, and it was equally nice and lined up perfectly - maybe yours was an outlier?
I abhor those clipsal connection things... I cut the wires and used open crimps and heat shrink.