Phorm is bad, bad, bad. Did I say bad.
BT are conning their customers by telling them it is to be a security tool (webwise) to eliminate phising etc and supply target advertising etc. All your browsing history will be supplied in real time to a company operating in China owned by a known spyware provider. and in turn they will bombard you with adverts.
You can of course opt out. But all your browsing history will still be sent to china. and in return BT, VM etc will get a kick back.
I am sure it is illegal under data protection rules and possibly human right rules. But until a test case how do you stop them.
If you run firefox there is a plugin under development to stop it at
www.dephormation.org.uk
other than that you would need to use secure proxies