Generally I don't like to publicly point the finger in cases like this, but this time I will: Tesco Compare, it's your turn.
I last used Tesco Compare a couple of years ago while looking for car insurance. About a year ago they began sending me promotional email, clearly realising they had a list they had not been using. I've moved to France and I'm really not interested in UK car insurance any more, so I wanted to unsubscribe.
The message they sent me shows they are handling my data correctly to some extent - they have my email address right, they addressed me by name. It also contains an unsubscribe link. That's the good bit over - It all goes downhill from there.