Thanks for the response Paulmc. Jadnashaunh actually sent me a manual with photographs of the process and yesterday I bit the bullet and had a go at fitting the towbar.
Removing the bumper etc was no problem. The disaster came when I bolted the towbar to the car. There are 4 threaded studs that protrud from the chassis to which the towbar bolts onto. The instructions state that the bolts need to be tightened to 108nm + or - 10%. 108nm is approx 79 lb feet. So I initially tightened all 4 nuts to 50 lb feet and then proceeded to try to tighten to 70 lb feet. Unfortunately my torque wrench must be faulty and failed to indicate anything over 59lb feet and I broke one of the studs off!
I can't believe now easily it sheared!
So now I have a major problem!
Don't know the solution to this as the stud is actually part of the car and is not removable. I can only guess it would be EXTORTIONATLY expensive to have put right by BMW.