Footwell full of water

[Benthomas]

A couple of weeks ago I noticed some water in my boot. Through removing all the carpets, seats and linings over the last couple of weeks, to find where the leak was coming from and to dry all the foam etc out (whilst also going insane), I have narrowed the leak to coming in behind the grey foam underneath the dashboard. I have had the glove box off and the pollen filter out, and checked the scuttle drains under the wipers which were clear but can not find where exactly the water is coming from. The water does not smell and none of my levels have dropped so I assume it is rain water. Whilst looking around the wheel arch I did notice that one of the fastening clips at the bottom was missing... i have ordered a replacement but could someone with better knowledge than me say whether this could be the cause? The car is a 2011 insignia. Thanks in advance for your replies