Interesting that after all this debate, i decided to drive to the Tandem shop at Ironbridge - they deal in Co-motion tandems. The owner sorted out a disc braked Tandem (with couplers) for me to use in the Alps and will sort out my frame this winter - cold setting it to a wider rear spacing and fitting either an Arai drag brake or disc.
All sorted as they say.
Thanks for all the help.
Tony