While it may seem like the copper was way out of line, I don't actually think it's as bad as it sounds. In fact, I reckon he's actually done you a favour by warning you that he's 'after you', as I can almost guarantee that you're going to stick to the speed limits for the foreseeable future. I'm also willing to bet that he knows this, and by giving you what appears to be a ridiculously harsh warning he's enforcing the law without needless paperwork and without actually giving someone points and a fine.
When I was younger I was in a similar situation, and it wasn't until I looked back and thought about it I realised that he was actually a really decent guy for saying what he did. Police these days know exactly what their limits are and won't step over them due to the litigation-happy society we've become, and this is his way of giving a big warning to you. Take it on the chin, remember the limits and don't speed.