Well after watching the video that Dell Gailey linked to I decided to fit some after market reversing sensors .
A very easy job as it happens , I went with a system that just has an audible alarm no led displays as I want to at a later date add a double din HU with reversing camera anyway.
Only difference I had was my sensors were 21.5mm and the holes in the lower bumper were much larger so a drilled out the blanking pieces and fit the sensors that way



still looks ok to me.

tried to mount the box as neatly as possible.


If you're doing this in an estate the reversing wire is the green wire with a black stripe. I broke into the loom here below the rear side window.


I also chose to mount the speaker under the boot carpet and face down into the foam...makes it sound much nicer rather than a screaming beep...beep...beeeeeep.

Thanks again Dell for the video link.

 

Glad it worked. That British guy does a really good job filming and explaining his work. He has a boat load of videos on fixing his Jag.