so it looks like you may have been looking at American procedures.
I wasn't looking at anything, I was going from memory and personal experience.
The Secretary of State (and anyone representing him) has a right to obtain details from all UK ISP's and doesn't need a warrant. If they fail to provide the details on request (or fail to keep satisfactory records), they can be prosecuted.
This was a law brought in when those ridiculous section ~40 terrorism laws came into effect, court orders are required to obtain account holder information, ISP's are required to store and provide certain information, they don't do it for free.
Most anonymizer sites are in the game of making money, they are much more cooperative than they would like users to believe, they don't want to lose their revenue by being shut down but they also don't want the users to know they cooperate either, so a cozy arrangement generally exist.
Duh. Good luck getting info from .ru or .in proxy services. Perhaps my example of anonymizer.ru lead you to believe I was talking about popular anonymizing services hosted in the US like hidemyass or proxify, I wasn't.
There are other methods of tracking a changing IP which are automated
You're talking about hitting nodes as they get routed or sniffing traffic? MITM attacks? those require a GREAT deal of infrastructure to be controlled or directly accessable by whoever is supposed to be tracking the changing IP. It's not realistic.
Its quite easy - the internet is bi-directional, you can't have a situation where you put a page request out on one IP and it arrives back on another without it being obvious that you pass an instruction for the expected return IP, otherwise it wouldn't know where to go.
SSH Tunneling? Proxychains?
If you use Modem access to a foreign ISP then it may start to get difficult, but not many would bother to get stuck with slow modem speeds again.
Ugh, no one would go to that much trouble when you can buy VPN access with virtual cc's or bitcoins for a couple dollars a piece. Interesting idea though.