There are several 'furniture projects' throughout the country. These aim to recycle furniture (and electrical goods) and often offer discounted prices to those in receipt of benefits.
In Yorkshire, these include the Keighley Furniture Project, the Richmond & Hambleton Furniture Store (also known as the Richmond & Catterick Furniture Store) and ReRun Development (Hull).
If you're not close to any of these, I'll add my backing to those people who've suggested the British Heart Foundation. They have large shops specifically devoted to the sale of furniture and electrical items. You can find your nearest shop by using the search facility here:
http://www.multimap.com/clients/places.cgi?cli ent=heart
Otherwise, you could simply contact a local auction house and ask them to collect and sell your items. You could then give the proceeds to the charity of your choice. The obvious choice would seem to be Crisis, which was originally set up (under the name 'Crisis at Christmas') to help the homeless over the Christmas period but now works for the homeless throughout the year.
Merry Christmas!
Chris