We have a tandem for sale. Viking Saratoga, upgraded with Avid BB7 and BB5 disc brakes. Only £150!
Also a Christiania Bike, complete with proper seat belts and folding bench seat. This has transported our 2 kids all around town for years - it's brilliant. £400.
The tandem looks like the one in this link (scroll to bottom of page):
The cargo bike is the Light model:
Based in NW London.
Email me if either tickle your fancy.
barnabyedwards at mac.com