Check out this Moulton APB Tandem on Youtube.
Moulton have never built a factory tandem, but several Mouton based tandems have been created as custom projects, by third-party framebuilders.
Several APB based tandems have been built by Doug Pinkerton. Here is one example of a Doug Pinkerton Moulton APB Tandem
See also an ATB based tandem in Australia
[...] This post was mentioned on Twitter by Jason_Cobb, patrick doocey. patrick doocey said: New blog post, Moulton Tandem – http://bit.ly/7p1boQ [...]
All these tandems I know are based on a Moulton ATB, not an APB.