How to actually effectively stop D2D:
Contact RM, I phoned the local sorting office and spoke to the manager's office, and tell them that RM will be trespassing if anyone comes to the property you legally occupy outside the terms of RM's operating licence.
Tell them the operating licence lets RM come to your door to drop off post, addressed and unaddressed. Their D2D junk is not covered by the licence. If they come onto the property for any other reason it will be trespass.
(How this stops the junk is on days when there is D2D junk but no post for your house, RM have to stop the D2D junk. As they go to great lengths, because of the trespass risk, the D2D junk stands to stop on days when there is post for your home, too. It is easier to actually stop all D2D than try and make it more complicated, to only do D2D when a specific house also has other post).
Tell RM trespass is a civil crime that does not need damages to be demonstrated in court.
Tell RM that trespass after being notified about trespass is a criminal act, aggravated trespass. You will call the police if RM come onto the property outside their licence. Staff being arrested will be a publicity problem for RM, and as RM is unionised the staff will have strong support. And likely RM letting staff get arrested for just doing their job will mean RM get sued by the employee/union.
All-in-all, this stops the junk much more effectively than RM's offered opt-out service. For the simple reason that there are possible consequences for RM, something that does not exist with opting-out.
This ingenious scheme is due to RM's customer service trying to fob me off in the past. They once tried to play a legalese jargon card to make me stop moaning about their junk, trying to talk about their operating licence and hoping I would think the law covered them. I looked into it and the licence does not cover RM's random business interests (as you'd hope), and so I confirmed to RM it would be aggravated trespass if they come here to dump junk only. The idea of using trespass law to stop junk is off this very site.
And pretty much from that moment the D2D junk actually stopped. I had been right up RM's complaints procedures god-knows how many times, but once they made things "legally" they highlighted their Achilles heel.
I moved house, and the first time the junk arrived I contacted the sorting office. And no more junk has arrived, at all. 2 months I've been here, one load, and that was before telling them no. Also, in two years my trespass notice will still apply. Another way this approach pretty much solves the junk problem.
This communiqué is either formal legal advice, or an internet anecdote. Take it as you will.