Best option is to either replace or install a beesting style aerial where the phone aerial usually goes towards the rear of the roof.
Hello Dave, there is already an aerial at the rear of the roof, I presume its for a phone. So if I replace it with a bee sting, will it come with the same type of cable to run the radio.
If you are not using tehphone aerial, then replace with ordinary beesting, but if you are using the phone, then look for a combined GSM/FM beesting.
Would`nt run the cable back to the radio though, much easier to run it down to the aerial booster (rear shelf) and pick up the connections there.
Have a look at the VW / Audi fitment aerials as I think the screw on Hirschmann style connectors may be the same as the one you are trying to connect to, failing that, let me have aphoto of the aerial plug you have, and I`ll find an adaptor. If you go for the amplified beesting, you should also be able to pick up a live supply from the aerial booster as well.