I came back to my car this afternoon and noticed a bit of plastic hanging off the underside of my car. It is just behind the front wheel arch. Not sure how I could have damaged it but any idea what the part would be and how much it would cost to fix/replace? I have attached some photos. Thanks

no idea, if it were me id either cable tie it up or remove it, car will not fall apart without it. Cost big fat zero

As above, pull off the bit hanging down, put it in the bin and forget about it.