In the event that you can't get rid of them here, there are a few nationwide charities that will even collect, who refurbish computers for charities. They may even be on the weblinks.
When our office replaced about 15 computers and monitors a few years ago it was a great way for us to get rid of them and know they weren't just going to be dumped.
I'll have to have a look. It's something obvious like Computers for Charity..but there are several. The one we used is, I think, based in Bude in Cornwall. They would arrange several pick ups in one area and then collect like that, so you can have to wait a bit longer, but it's well worth it.