Awesome feedback chaps, thanks so much!!
Comanderfish; I had one of those hideous Halfords specials on my Z4 for a while, it was truly awful and took an age to get on safely plus I did get scratches, though not from the bikes but from the rack itself! -Also anything in the boot stays there until you take the whole rack off which is a pain in a small car with the only storage in the boot
Johnspiderman; t'would be fab to find out if such a fitting port/s exist/s
I've now checked with most of the towbar makers and PCT are the only ones considering making a towbar for the Brera /Spider though when I talked to them they were not very confident that production would ever start as the EC approvals cost are so high and with the sales numbers probably not vast it may no make sense (their words not mine)
However I've found a company that specialise in making towbars for specialist cars and those that the big towbar makers do not support. They do them for Bentleys and Astons!.
A very helpful chap (with a 5 week waiting list for specialist towbars!) explained that they could make one for the Spider but that it could only be used for the bike rack and not towing as it would not be EC certified. cost approx 500 quid plus vat inc including electrics.
They need to have the car for a day in order to do the work. I insisted that the bumper should not be cut and that the bar be detachable. all of which seemed to be no real issue (subject to looking at the car). I'll carry on checking this out their web addy: Watling Towbars Bespoke Manufacturers of Towbar and Motorbike and Cycle Carrier Systems
Helpful chap at Watling Eng did say that it was unlikely Alfa would ever homologate a towbar fitting for the Spider so I suspect no tapped mounting holes etc exist...