Rear fog Reverse light removal.

Just acquired a neglected 2011 R56 Cooper Diesel which we're in the process of making good. Mechanically sound, but not well loved. We've found the reversing lights in the cluster don't work and the Fog light is giving an intermittent error on the dash. I'm suspecting it's been parked in a flooded area and the light might have been submerged as the front fogs also show some damage. Try as I might however I cannot get the rear light cluster to budge. There are clips that I have squeezed, pulled, pushed etc and the thing is stuck fast. I've scoured Youtube, asked on Reddit but I can't seem to find anyone with the know-how to get the damn thing out. I just want to remove it so I can properly inspect it and decide if I need to replace the whole unit. From the user manual and the best shot I can get from the rear. The manual seems to be pointing to the small grey clip next to the larger black part, but I've tried squeezing them but they won't budge. I also think that's just for the bulb and not the removal of the entire unit. There's also the issue that the LH side unit is almost inaccessible due to some heat shielding under the car. Any help greatly appreciated.