Did some googling, came up with:
"cycle-link" bike joiner [Archive] - Bike Forums
Bicycle to tandem converter - Patent 5860662
but no discussion of how well it worked. I had the same idea a few years back (We mediocre minds can think alike too LOL) and bought some hardware to test it, but never got it all together. Didn't know it was patented. Not sure if the U.S. patent is by the British inventor or not...