The items that fit your MG MG3 are shown below.

On MG3s with DAB from the factory, this is not handled by the original head unit, there is a seperate receiver which decodes the DAB input and feeds it to the head unit as an analogue signal. The DAB module is located in the passenger (near side) foot well behind a trim panel on the back of the centre console which is held in place with a plastic trim clip.

Remove the panel and the DAB module is visible behind. The green Fakra E connection going into the module is the DAB antenna, use a 21-037 (Fakra to SMB antenna adapter and a fakra extension to connect the original DAB antenna to the back of a new after market radio with DAB.