Further to yesterday's story about junk mail this is now breaking news on the Royal Mail web site:
You can choose not to receive unaddressed items we deliver on behalf of local and national businesses (this may include communications from local and national government)
The address to write to for Door to Door opt outs is:
Door to Door Opt Outs,
or email: email@example.com
Here's something I found on Rob Hinckley's web site:---
Please be aware (Royal Mail don't tell you this) that the opt-out will lapse after one year, at which point you'll have to do it again. Also, this is quite different from the addressed junk opt-out available via the Mail Preference Service.