So its turned into a bit of a minefield of randomness. I have 2014 Golf Mk7 (pretty standard, nothing fancy)
For a detachable tow bar with car specific electrics
VW dealer - £735 all in
Essex Towing - £515 + plus some VW bumper trim piece, £100 circa = £615, plus a few trips to collect part and leave car in Essex.
GT Towing (Recommended by someone here) - £962 all in
I think I might just go with the VW dealer to avoid the hassle of saving £100.
No idea how much the actual towbar costs, maybe like £300? Most people claim its a 3 hour job.