As I understand it, the legislation is about allowing the record companies to finger internet users, and be able to legally force ISPs to ban the internet users based on company evidence alone (presumably on the basis that the user has breached the ISP terms). Whether users could migrate would depend on the law - would the banning ISP have to provide a MAC code, and would they (or the record companies) be allowed to share info on banned users (would raise legal issues if not covered explicitly in the law).
Problem1: identifying copyright violation (especially if encryption is used)
Problem2: linking violation with an ISP account (dynamic IP, wifi stealing, etc)
Problem3: linking violation with a person (teenage son downloads something, dad loses home business?)
Problem4: proving intentionality (trojans, downloading wrong thing, etc)
All of these are non-trivial (except possibly the last one - you can probably legislate it away by declaring it doesn't need to be proved). They'll probably pass the law anyway. Question is, what will they do if/when the first case of mistaken ban is publicised?
Incidentally, aren't there perhaps Data Protection issues over record companies accessing P2P data?