Random panel name?!

Had a shunt up the rear earlier today, am trying to figure out how much its gonna cost to repair, but i was wondering if the little bit under the tailgate had a name?! Coz it's pretty badly dented and is going to need replacing. The only thing i cant work out is if its separate or attatched to the rear panels either side...

Can someone help?! Email is probably the best way to contact me, [email protected]