UKSF Photos - Unknown UKSF in Iraq

Bit of a mystery this one: photo from post-invasion Iraq showing US Special Operations forces (background) accompanied by, most likely, a member of UKSF. He is wearing US clothing but a British helmet and comms gear and is carrying a L119A1 (C8 Carbine). Which unit - SAS, SBS, SRR or SFSG) is unknown.