Welcome corkgsxr to Berlingo forum.
May I draw your attention to this information copied from the Departmant For Transport website and I quote,
"4. What are the requirements to fit a type approved tow bar?
If you wish to tow anything with a car which was first used on or after the 1st August 1998 the car must be fitted with a type approved tow bar.
5. My car was first registered on 1st September 1998; do I need a Type approved tow bar?
Yes, all cars first registered on or after 1st August 1998 must be fitted with a type approved tow bar if they are to be used for towing.
6. How can I tell if a tow bar is type approved?
Each type approved tow bar will have a label, plate, or stamping detailing its type approval number for example E11xxxxxxx, and the details of the vehicle for which it is an approved fitment.
7. May I fit a type approved tow bar myself?
Yes provided you use the car manufacturer's approved mounting points, and follow the tow bar manufacturer's instructions."
So clearly, the home manufacture of towbars is no longer permitted, I have recently had a Witter towbar fitted to my vehicle, this is type-approved and all holes matched up with ready drilled ones in the chassis.
I am not in any way doubting your ability to fabricate and weld materials but just pointing out that laws have changed and in the event of an accident then not only do you risk the attention of the police but also you would undoubtedly invalidate your insurance.
To make you further aware, towbars now form part of the current annual M.O.T. test for vehicles in the United Kingdom