These were, I think, published in Metro (free newspaper). I am noting them here for reference. I have no knowledge of them other than their reported existence.
For a more comprehensive list of collaborative consumption enterprises, see http://www.collaborativeconsumption.com/directory/. There are lots if collcon enterprises about, many of them overlapping in the service they are sharing. I think a shakedown is needed.
I don't want to be naive or offensive, but it strikes me that some of these may be helpful to those facing "bedroom tax".
www.storenextdoor.com - rent out loft/garage space to someone looking for storage space.
www.spareroom.co.uk - rooms to rent Monday - Friday for commuters
www.rentmyitems.com - rent out tools and DIY items
www.parkatmyhouse.com - rent out a private parking space
www.gocarshare.com - matches passengers with car drivers for journey cost sharing
www.taskhub.co.uk - search for odd jobs tradespeople.