I am selling a bike trailer, similar to the one shown here (slightly older style wise and different make - photos on request if you want):
[url]http://www.amazon.co.uk/Adventure-St3-Steel-Two-Seater-Trailer/dp/B001OC6CEG/ref=sr_1_9?s=sports&ie=UTF8&qid=1290594290&sr=1-9[/url]
It can seat 2 children, has quick release wheels and folds flat for storage. Cost me around £100 new.
It's 2 years old so does have some signs of use but is a bargain at £30.
Collection from Croydon, I may be able to deliver locally.