Re: The Labour Party...
Partly related.
Something I'm seeing a lot more is the: "By <interacting with us in some way that hands over your personal details> you consent to us contacting you for marketing purposes. If you don't want your details used for these purposes please contact us by <postal address> to opt out".
In other words you cannot tick (or untick, or "don't not untick the box if you never want to not get our advertisers' shite") the box to opt out at point of first contact. You have to go to the added effort of contacting them separately after the first contact. Make it harder to opt out and fewer will bother. I can't see how this is informed consent when the only way to withhold that informed consent it not dealing with them in the first place.
Worryingly I find this more prevalent with Charities so I don't donate to those which pull this nasty little trick. My donation is the money I give you not my personal details for you to flog off to all and sundry via your marketing dept.