As a direct result of BT's infuriating dalliance with the despicable Phorm system, I chose to leave BT, and joined Zen Broadband, with the switchover on 8th October. 

I selected Zen from the myriad of other ISPs out there for several reasons - good reviews (in both press and in the internet); reasonable pricing; clear upfront description of service; rapid response to my equiry about Phorm; no lock-in to lengthy contract.

Over the first week of being with Zen Broadband, I've been very satisfied (having said that, over the years I was with BT Broadband, the service was generally good as well).  Specific points:

• Increased download speed.  As I posted earlier, by download speed increased from 1.9 Mbps with BT to more than  6Mbps with Zen.  I've tested this at different times of day, and it seems to be consistent.
• No Phorm.  I emailed Zen about this and they confirmed no plans to implement Phorm.  I appreciate commercial pressures may force them to change - if that happens, I'll be on my way as I only have a 1 month commitment
• Zen have an excellent Customer Portal for monitoring and setting up all sorts of aspects of their broadband service.  As I write, I am still investigating what's available.
• As far as I can see, my btinternet.com email address is still functional, presumably because it's run by Yahoo!

I did receive a peculiarly worded letter from BT about my upcoming departure from BT Broadband on 8th October (bizarrely not delivered until 11th October), and suggesting I rethink my choice, and making it sound as though my phone line would be disconnected when the switch was made.  This is patently not the case.