The UK constitution is (and this is debateable of course) based in part on the concept of 'parliamentary sovereignty' - one commentator put it that 'parliament could make it legal to kill blue-eyed babies'. Since UK entry into the EU, passing of the Human Rights Act 1998, and the Scotland Act 1998, there are things it cannot do with its laws (until, like David Cameron proposes, Parliament does away with those laws, to get back to the blue-eyed babies position). As things stand, the only testing of a law is a declaration of incompatibility with the HRA or EU law. Sadly a lot of powerful new EU law (under the Lisbon Treaty) doesn't apply to the UK (or Poland - both got waivers to certain treaty obligations).

To answer the second part of your question, I think the proposed Bill includes a provision for you to appeal a disconnection. There's also the interesting possibility of a business suing an ISP for damages after a wrongful disconnection (which, given the way this Bill is so poorly structured, I would expect will happen)... what would the ISP then do? TalkTalk, who started this petition, isn't happy (but doesn't mention this reason in the petition description)

Frightening to think how easily a rival could have any YC business based in the UK disconnected, through weak Wifi security or any other means of making it looks like that business is infringing this new proposed law.