For the benefit of any future Google traveller the specific clip you need is part number 8231533020.
The OE clip has a foam washer which can be easily transferred onto the new clip.
In my case the clip was probably damaged because the bolts holding the spoiler had come loose. Make sure you tighten those up and use some loctite to make sure they dont wriggle themselves free again. There are 3 bolts behind the top inside trim of the boot lid and another 2 either side behind rubber gromits.