After weighing-up available options, I opted for the DIY route.
Westfalia Swan Neck Tow Bar from PF Jones (eBay) £106.99, del'd
Seat specific OEM tow bar loom from PF Jones (eBay) £137.00, del'd
The tow bar kit comes with full (pictoral) fitting instructions, but assumes that the rear bumper has been removed. A 'bumper cut' has to be made in the lower apron section, but this is pretty easily achieved.
The OEM loom circumvents the need for cutting and splicing into the electrics and is a self-contained unit that works in conjunction with the vehicle's ECU. It includes all necessary safeguards to protect the vehicle's wiring in the event of failure/malfunction.
A 'dealer download' is advised at the service interval following installation to reconfigure the parking sensors and other ancillaries, but the installation works perfectly well in the interim.
Fitting the loom requires patience and a methodical approach, with large sections of interior trim requiring removal to complete the job properly. Full installation instructions are included by the manufacturer which, if followed properly, make the job well within the capabilities of a reasonably competent DIY'er.